[CONSOLE] keeping entity with UUID spam

Does MC-88922 describe this issue ?

Please attach the complete console output to this ticket.

reopening, this issue is actually duplicated by MC-98027

Have been seeing this a lot in my server's console since 1.9 and have realised that two reported missing horses, which I had already worked out were just invisible with non-functioning AI.

I have a pen with 3 horses, 2 of which are invisible and do not seem to have functioning AI. I can /tp to them, however, which is the only way I could confirm they were indeed there, and do not seem to move at all.

[16:04:52] [Server thread/WARN]: Keeping entity EntityHorse that already exists with UUID 8671f013-891f-45c8-af9c-cf8f786035a1
[16:04:52] [Server thread/WARN]: Keeping entity EntityHorse that already exists with UUID 8671f013-891f-45c8-af9c-cf8f786035a1

One of the three horses is visible and moving, the other two are invisible and not moving. I assume the two duplicates are just not being fully loaded because they have duplicate UUIDs.

I have seen the messages a ton since updating to 1.9, and just assumed they were resolving issues and would eventually stop - but if this is happening across the world then it' a pretty serious problem for many players, and indeed the server since many of these duplicate entities will likely just never go away.

Something to tinker with for the devs: A copy of my affected vanilla game files (last time used with server 1.8.9 and not loaded into 1.9 so far) at https://www.dropbox.com/s/y3iqdvoryvi6fak/Cubystar_World_1_8_9_March2016.zip?dl=0

I have the same problem on my server, no crashes, but the map is very laggy.
The error appear after an 1.8 world converted for 1.9: "Keeping entity Entity[...] that already exists with UUID [...]" and affect all mobs.
That problem is not from my host, it's very efficient and work perfectly on 1.8.

I've tried some test:

• repeat /kill @e[type=!Player]

• try to load my map in singleplayer

• try the many 1.9 snapshots, and 1.9.1 pre-release 1,2,3
  No test is really conclusive, the game is very unplayable, particularly the IA of mobs, breaking blocks, eating and redstone systems

Personally, I think it's similar with the invisible skeleton in snapshots.

[I post that I've write on the closed post MC-98027.]

I attached a game output which at first there is console spammed with "something's taking too long! (MC-96120)" , before it is spammed with "keeping entity with UUID."

1.9.2 confirmed

This message has been spamming my server log heavily since I replace the minecraft_server.1.8.9.jar to 1.9 keeping the rest of the server files from the old version. I was able to kill some of the entities using /kill UUID command, but the same" keeping entity..." warning messages for that particular UUID still show up. Also, I was unable to kill most of the entities with the UUID that shows up in the warning message, because "That entity cannot be found". I've been seeing this error for any kind of entities including MinecartHopper, VillagerGolem, Villager, etc.

Same situation for me. Minecraft vanilla server (no mods, no plugins). Spam begun when I updated the server from 1.8.8 to 1.9.2.

This is my server log.

I don't know if it's relative to this issue : MC-94438. However server lag is a massive issue in 1.9. My server log is also spammed by this "Keeping entities".

Same happened to me when i upgraded from 1.8.8 (double checked right now) to 1.9.2

This started happening to me in my world when I upgraded from 1.8.8 to 1.9. I'm running 1.9.2 and it's still happening.

[Server thread/WARN]: Keeping entity EntityHorse that already exists with UUID 2c4026c1-1fc1-462a-8ad5-ad71d4d459ad

I had this problem after i made an upgrade on my server from 1.8.9 to 1.9. I am receiving tons of warnings about entitys with certain uuids, and i cannot remove them through command lines (/kill <mob uuid>, /kill @e[type=<mob name>] and /kill @e[!Player]), it seems that the same uuid is not removable from the list, and i have a lot of mobs in this situation. It says that i have killed the mob but after some time it happers again. This result in CPU usage of almost 100%, and after a while, it crashs, and the server restarts.

18:12:25 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:12:25 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:12:25 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:12:25 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:12:25 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:12:49 CONSOLE: [INFO] Killed Horse
18:13:18 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:18 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:18 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:18 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:18 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:45 CONSOLE: [INFO] Killed Horse
18:13:56 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:56 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:56 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:56 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:13:56 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:14:13 CONSOLE: [INFO] Killed Horse
18:14:42 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:14:42 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:14:42 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:14:42 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:14:42 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:15:24 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:15:24 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:15:24 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:15:24 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28
18:15:24 CONSOLE: thread/WARN]: Keeping entity EntityHorse that already exists with UUID 24ec0e25-2c6e-45b6-acae-d3754afc8a28

1.9.3 confirmed

How can be that no one have yet started to repair this critical bug for old worlds, and are already adding more stuff in the game to prepare it to 1.10!!!!

I am playing in a server with almost 3 years old with my friends, and me and my friends have each one has an youtube channel where we post the meanwhile of our lifes in the game, and we are unable to update the server because of this bug. Each one of us have an average of 40 days of playing in this world, we are not playing around here!

If we have to reset our world, at least me will quit from playing minecraft for real!

The amount of lines that we get spammed on the server console because of bug is pretty ridiculous. There were other problems with the server upgrades too. When I upgraded my server from 1.8 to 1.9, the ender dragon fight was broken even after deleting the DIM1 directory, so I had to manually edit the DragonFight attribute in level.dat to fix it. Please put more thoughts into the upgrading process.

Still happens in Snapshot 16w20a.
Also, for some reason I only get Villager and Sheep errors(also in 1.9 where I started getting this issue)
Even more confusing: it only happens when I enter or leave a specific region in the world, which was generated after updating my server to 1.9.

It seems that i get a WORK AROUND for this bug!

I believe that this bug comes from previous version as 1.7 and before that, since i already had some problems, passing from 1.7 to 1.8, where we had some mobs spawning inside of blocks, and get some warning about it (dont remember the name of it). In that time we had executed the kill command, and we where able to solve the problem.

My server maps (overworld and nether) where generated in 1.6.2, back in setember of 2013.

So, to solve this, i started in last stable version, the 1.8.9 and edit the server.properties file, in the following lines, to avoid any type of spawning mobs:

difficulty=0 # with spawn-monsters=false this command does nothing but i had it in 0 at the time, because i was doing other tests before without sucess.
spawn-monsters=false
spawn-npcs=false
spawn-animals=false

Then i made a trip where i had "civilization" in all worlds, where we had mobs with alternative names. After that, i update my server to 1.9.4, and i notice some warnings (but serious less than before) of 'keeping entity', with all the spawning parameters in false⚠️ , and i executed the kill command through the uuid (/kill <mob uuid>) of the mobs in the warnings, some of them it was possible to kill. After doing this, i reach a point where i didnt get any warnings anymore, in the areas where i had before. Then i change again the spawn parameters:

difficulty=2
spawn-monsters=true
spawn-npcs=true
spawn-animals=true

And made again another trip in my worlds, and it was all fine, without any warnings. Now i just have to repopulate all the farms that i had working with mobs before through creative mode.

Its better then a full reset !!!!! =D

Hope that this could help you guys.
Cheers from Portugal.

I've had this problem on a server for a long time, just figured out how to fix it. Just teleport the UUID to yourself, sometimes i got an animal that was alive, sometimes just the death animation, then the spam stopped. (Kill appears to work in console, but it really doesn't)

I had same "keeping entity..." stuff. I killed 2-3 of them. One of them was an iron golem, i killed it with kill uuid and replaced it by another one (built it, not summoned), but when i came back to that area of map, it was back alive. After second killing it seemed to work.
I also killed a sheep and a villager, but since i did all this, i get 30-40 lines of "Fetching addPacket for removed entity".
Any clue what i can do against this or what that means?

Confirmed for 1.10.1

I have the same problem and I'm no longer able to play the game on my server. Please help!!!
Client and Server version: 1.10.2

Here the full description of the problem:

http://www.minecraftforum.net/forums/support/server-support/2715194-keeping-entity-that-already-exists-server-version
Ok, I made the mistake to update this buggy game from 1.8.9 to 1.10.2 (Server and Client) and the server gives me error messages like:

[18:37:23] [Server thread/WARN]: Keeping entity Pig that already exists with UUID c7c7fc74-bdca-4d43-a135-69bb3d257d0f
[18:37:23] [Server thread/WARN]: Keeping entity Cow that already exists with UUID c0a0ac0d-3491-44bc-a4c1-71c633cb8fb5
[18:37:23] [Server thread/WARN]: Keeping entity Cow that already exists with UUID 1752c06a-b982-43ac-a323-fb0cd6b0379d
[18:37:23] [Server thread/WARN]: Keeping entity Sheep that already exists with UUID 908d49b9-a0f7-4709-aeac-b0a6c0528089
[18:37:23] [Server thread/WARN]: Keeping entity Cow that already exists with UUID 1e4c5bb0-ab4e-499e-bfd4-6a6ed5c8c37f
[18:37:23] [Server thread/WARN]: Keeping entity Sheep that already exists with UUID a58cf73c-99c0-4697-aed5-f63d40fd0804
[18:37:23] [Server thread/WARN]: Keeping entity Sheep that already exists with UUID c64c4d5c-274a-4efb-8500-6417a96cd7ec
[18:37:23] [Server thread/WARN]: Keeping entity Sheep that already exists with UUID 3a89e16e-d7d9-41cb-be6d-273936cf40a0
[18:37:23] [Server thread/WARN]: Keeping entity Cow that already exists with UUID cbc367f3-9a5f-4352-a575-962189c57fb8
[18:37:23] [Server thread/WARN]: Keeping entity Cow that already exists with UUID 6fd32058-c6a8-4ef7-a6e2-f9d697d264a4
[18:37:23] [Server thread/WARN]: Keeping entity Sheep that already exists with UUID 6f224a6f-f54f-4158-8add-d77fc7fc1926

After a while the Server gets more and more laggy and I lose connection to the Server which runs on my own machine. So, who shall I congratulate for this programming achievement?

Is there a remedy for this nonsense? How can I get my paid game to work as intended? Please help!
P.S.: If I try to kill the things with in the console with "/kill 3882a1be-00c0-4a58-b432-5c31f4503b94" for example, the server tells me, the mob is killed. So I killed all problematic entities, restarted the server and behold, all errors came again.
So, please help!

Maybe interesting too:
If I stop the server, I get:
stop

[15:53:41] [Server thread/INFO]: Stopping the server
[15:53:41] [Server thread/INFO]: Stopping server
[15:53:41] [Server thread/INFO]: Saving players
[15:53:41] [Server thread/INFO]: Saving worlds
[15:53:41] [Server thread/INFO]: Saving chunks for level 'world'/Overworld
[15:53:41] [Server thread/INFO]: Saving chunks for level 'world'/Nether
[15:53:41] [Server thread/INFO]: Saving chunks for level 'world'/The End
[15:53:41] [Server Shutdown Thread/INFO]: Stopping server
2016-07-24 15:53:41,994 ERROR Attempted to append to non-started appender File
2016-07-24 15:53:41,996 ERROR Unable to write to stream logs/latest.log for appender File
2016-07-24 15:53:41,998 ERROR An exception occurred processing Appender File org.apache.logging.log4j.core.appender.AppenderLoggingException: Error writing to RandomAccessFile logs/latest.log
at org.apache.logging.log4j.core.appender.rolling.RollingRandomAccessFileManager.flush(RollingRandomAccessFileManager.java:109)
at org.apache.logging.log4j.core.appender.rolling.RollingRandomAccessFileManager.write(RollingRandomAccessFileManager.java:90)
at org.apache.logging.log4j.core.appender.OutputStreamManager.write(OutputStreamManager.java:129)
at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:113)
at org.apache.logging.log4j.core.appender.RollingRandomAccessFileAppender.append(RollingRandomAccessFileAppender.java:96)
at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:99)
at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:425)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:406)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:367)
at org.apache.logging.log4j.core.Logger.log(Logger.java:110)
at org.apache.logging.log4j.spi.AbstractLogger.info(AbstractLogger.java:1011)
at net.minecraft.server.MinecraftServer.u(SourceFile:381)
at net.minecraft.server.MinecraftServer$2.run(SourceFile:738)
Caused by: java.io.IOException: Stream Closed
at java.io.RandomAccessFile.writeBytes(Native Method)
at java.io.RandomAccessFile.write(Unknown Source)
at org.apache.logging.log4j.core.appender.rolling.RollingRandomAccessFileManager.flush(RollingRandomAccessFileManager.java:106)
... 12 more
2016-07-24 15:53:42,032 ERROR Attempted to append to non-started appender ServerGuiConsole
Exception in thread "Server Shutdown Thread" org.apache.logging.log4j.core.appender.AppenderLoggingException: Attempted to append to non-started appender ServerGuiConsole
at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:89)
at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:425)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:406)
at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:367)
at org.apache.logging.log4j.core.Logger.log(Logger.java:110)
at org.apache.logging.log4j.spi.AbstractLogger.info(AbstractLogger.java:1011)
at net.minecraft.server.MinecraftServer.u(SourceFile:381)
at net.minecraft.server.MinecraftServer$2.run(SourceFile:738)

Thank you very much for editing my Post! 😀

Still seeing the same issue on server console, ver. 1.10.2. No mods are being used, currently running with max of 3 players. Server repeatedly reports the "WARNING Keeping entity Villager with UUID" etc. message in a given chunk area. When these messages are appearing, using /KILL on that UUID reports that the entitiy cannot be found, yet the warnings persist.

Doing /kill uuid on all of those entities is not a feasible solution. There are simply too many players on my server with villager shops, iron golem farms, and etc. I cannot just kill hundreds of villagers and animals without breaking their farms and replace their villager with a new villager that sells the same items.

Funny, all comments deleted, when posting that you are not satisfied with this company... No support when new versions of the game are not working properly, but the customers money was taken with pleasure...

Maybe because this is not the place to voice your general disappointment with the company. That's why we have a forum.

Well, that would be right if we would get a response in the forum for that matter...

I got no help here:
http://www.minecraftforum.net/forums/support/server-support/2715194-keeping-entity-that-already-exists-server-version

I got no help in this thread and I wrote an E-Mail to Mojang support and you guessed it, no answer there.
What would you suggest to do if your paid game is not working after an update and you get no help?

This site is not a discussion or user help forum, it`s a bug tracker. Comments not contributing anthing to the bug will be deleted.

Thank you for responding, [MOD] Kumasasa!

I agree, this is a bug tracker but please understand that people get frustrated after 8 months of a known bug is not worked on
"People: Assignee: Unassigned"

and we get no help. Thank you for considering this, we can't play our game and still nobody is working on that bug! Have a nice day.

Same problem here... this started yesterday... with some zombies...
and now with zombies and sheeps, we just got 5 people online and whole server crashed with Java errors.

Not sure if the java errors where related.. but I will dubble check first..
I'm running MC 1.10.2 Vanila

Same issue on my server, however, this is with a brand spanking new server running 1.10.2 and with a brand spanking new map to boot.

Thank you Ray Herring, that might be a very useful information for the Developers, that a new map also suffers from this bug. Because I got told several times to just delete my map I built with friends over years.

@unknown, the world you provided contains already entities with duplicate UUIDs. I assume in earlier versions the game did not test if another entity with the same UUID already exists when adding loading or creating an entity.

This MCEdit filter "fixes" the duplicate UUIDs.

Chances that the same UUID is generated twice are pretty small which means that these entities where somehow duplicated or somebody changed their UUIDs. @unknown's world contains items with the same UUIDs as well which makes it unlikely that this happens to mobs only.

Please provide a way to reproduce this entity duplication if you found one. If someone with a map created in 1.9 or higher, which was never opened in older versions, experiences this bug, please attach your world or link to a download page.

Maybe relates to MC-70860

I found a simple work-a-round. I was having this issue in my 1.10.2 vanilla server. I had 4 or 5 zombies generating this error.

To fix the issue, I changed the server to difficulty 0 (Peaceful) and gamemode 1 (Creative). After flying around reloading all the chunks near spawn, I exited the game, saved the word, and restarted the server.

The errors have now stopped. I assume the zombies were deleted when the chunks were loaded in Peaceful mode.

Maybe relates to MC-70860

Linking to this comment might be helpful as it contains also a link for a MCEdit filter which should be able to "fix" this bug.

Can confirm that this is still an issue in both 1.10.2 and snapshot 16w39b 100% Vanilla servers.

Not sure if there is really a solution for the warning spam. The warning is eligible and deleting the duplicate entity might cause problem if the player interacted with it at some point of time.

I suggest only changing the affected version if someone experienced it in a newly created world. Once the source is found the fix could include assigning new UUIDs for duplicate entities once.

I have only recently updated my vanilla server from 1.8.9 to 1.10.2. During this update I ran the world in a modded instance and used a mod I made to remove all the duplicate entities from the world. The first times running the actual vanilla server after this, everything was fine and I got no warnings in the server console.

However I just now looked at the server log, and at the moment there are 4334 lines of this warning message, 4331 of those lines are for Sheep entities. (There are small sheep farms near our server spawn). I started the server and immeadiately got a few warnings of duplicate sheep entities (so they must be in the spawn chunks). This seems to become a real nuisance because of the warning messages constantly polluting the server log...

But the real issue that should be fixed is the fact that entity saving is currently, and has been for a long time, broken. Sometimes when entities cross chunk boundaries (probably near to a time when the chunk unloads?), they can either duplicate or vanish. I saw a youtube video recently where the person said that the entity may get saved to both chunks, or neither, which would make sense. My Mojira-search-fu is failing me, does someone know if there is an open issue for this entity saving bug (vanishing/duplicating entities)? In my opinion it is the most serious and game breaking bug currently in the game, and it has existed from personal experience AT LEAST since 1.7.10, probably even a lot longer (always?).

@unknown, MC-16009 is probably our oldest issue that describes that problem, but it contained little information and was never maintained. MC-108469 describes one possible way that entities may be lost on chunk unload. I'm not sure it covers duplication or all possible causes, however.

In 1.11.2, Didn't get spam but 1;
Keeping entity minecraft:chicken that already exists with UUID 6a45f4ce-92e8-4c71-97af-c632182d092d

New world in vanilla 1.11.2 and the bug arrives after a few minutes and the server becomes very slow before crashing.

[09:18:26] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 0c036f89-72b5-44e3-b9b1-da3814bc9956
[09:18:26] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 9bdad6ab-7d8e-47f5-9b87-ae92af068d02
[09:18:28] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[09:18:28] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[09:18:28] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[09:18:28] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:22:10] [Server thread/WARN]: user moved wrongly!
[09:23:22] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:24:19] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:25:04] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:25:15] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 0c036f89-72b5-44e3-b9b1-da3814bc9956
[09:31:49] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 0c036f89-72b5-44e3-b9b1-da3814bc9956
[09:31:58] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[09:32:10] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:32:19] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[09:32:36] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 9bdad6ab-7d8e-47f5-9b87-ae92af068d02
[09:32:39] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[09:33:33] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 0c036f89-72b5-44e3-b9b1-da3814bc9956
[09:37:46] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 0c036f89-72b5-44e3-b9b1-da3814bc9956
[09:40:46] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:41:28] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[09:43:12] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:43:26] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:44:06] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:44:43] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:45:07] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:45:32] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:52:19] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:52:19] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 9bdad6ab-7d8e-47f5-9b87-ae92af068d02
[09:53:22] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:54:29] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[09:54:29] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[09:54:39] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[09:55:05] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:55:17] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[09:55:35] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[09:55:35] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[09:55:49] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[09:56:07] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:57:57] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[09:59:22] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[09:59:29] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[09:59:44] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[10:02:49] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[10:06:38] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[10:06:49] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[10:06:54] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[10:10:12] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[10:10:51] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[10:10:53] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[10:11:00] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[10:11:28] [Server thread/WARN]: Keeping entity minecraft:cow that already exists with UUID 23cda45e-9e7f-4be2-8966-dcd144f50704
[10:13:38] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 920ff0d0-1cfa-4723-8d30-935b88a06528
[10:14:06] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID c1eb724f-e764-4cb6-9cef-a5d05a36591f
[10:14:12] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[10:15:03] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b
[10:23:39] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[10:26:44] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 854a98db-5e37-4084-bf9d-b9ba238b4ae3
[10:27:14] [Server thread/WARN]: Keeping entity minecraft:pig that already exists with UUID 3d48bbf8-7bcb-40da-ba20-49d33ecf0f6b

Happening on a vanilla pc server 1.11.2 with minecarts. I have removed all minecarts and minecart items from loaded chunks. The warning messages still appear.

I was getting this on my server after upgrading from 1.8 to 1.9 and then to 1.10. Thinking there was corruption, we restarted a brand new world in 1.11 and are still seeing this entity log message spam. How is this not fixed after so long? I've seen numerous bug reports opened, and most, if not all, are showing "Resolved" but they clearly aren't.

@unknown, you should look at Resolution, not at Status. Most likely all of those issues were resolved as "Duplicate", as they describe the same thing as this ticket, so they aren't worth to stay Open.

This bug clogs up my console/log and impacted the operations of my server quite a bit. I gunzipped the entire log directory and did a grep count on this;

grep -o '[Server thread\/WARN]: Keeping entity' * | wc -l
2453079

As you can see there are 2,453,079 hits! It really makes it unpleasant for me to monitor the server, and I am sure this had affected the other admins of vanilla servers as well.

@Takuto Lehr, If you want to fix the current continuous log spam (ie. clean up the current state of the world), there is a Forge mod that allows you to do it with relative ease, here: https://minecraft.curseforge.com/projects/world-utils. I have done the clean-up operation twice thus far for my vanilla server's world.

The problem here is, that because of the entity handling issues that are currently in Minecraft, the entities can over time duplicate again and then the log spam can start to happen again. So unfortunately you might have to do the clean-up/duplicate removal operation periodically, until hopefuly some day the entity handling issue itself gets fixed. This issue report is just a symptom of that entity handling bug.

One way to mitigate the problem, is to modify things like animal farms (which often have large numbers on entities) so that the animals can't move across chunk boundaries (F3 + G helps with that). Because afaik, the entity duplicating issue happens when entities move from one chunk to another in the same tick (or very close) to when a chunk unloads or becomes a non-entity-processing chunk (ie. when a player moves away from the area).

@Matti Ruohonen, thank you for the suggestion, but does the command remove-duplicate-uuids actually /kill the entity? I was wondering if this operation somehow reassigns an uuid to the entity with the duplicated one. If it does kill, then it is not a viable solution for me, because I just cannot destroy the villager shop, farms, and etc that my players spent years to build. If I could kill the entities then I could have just periodically piped the output of the grep command to console to kill, or used the MCEdit to clean it up.

Secondly, I have to admit I do not know anything about Forge or any mods, but I care very much about staying vanilla, and being able to update the server as soon as the new version comes out without worrying about any of the mods being outdated. For that reason I do not want to install mods of any kind.

@Takuto Lehr, It doesn't do a /kill per-se, because it does the removal directly from the chunk NBT data. The end result is essentially the same - only one entity of each UUID will be left. Since UUIDs are supposed to be extremely unique, a case where two different entities would have the same UUID is almost non-existing, so removing all but one entity of each UUID should always result in leaving one copy of each what is supposed to be one entity. But there is no control over which one is left. Thats should really only make a difference with things like villagers, if they duplicate before all the trades are unlocked, or with mules that contain items in their inventories etc. But the same issue also exist while normally in-game - depending on in which chunks the entities are and in which order the chunks load, the entity that will "exist in the world" is also non-deterministic in a way (because only the first one can be spawned in the world, the rest print out that console warning and won't be spawned in the world, but they will still exist in the chunk data, and thus they won't disappear on their own). But that is what you end up with when dealing with a result of a bug that duplicates data...

While you need to have Forge installed to use the mod, you can still keep the world entirely vanilla. All this particular command does, is remove the NBT tags containing the duplicated entities from the chunk's entity list. So to use the mod, you can either temporarily install Forge and the mod to run the command on the server (which is more or less how I did it), and then remove Forge again, or you could have a local Minecraft instance with Forge and the mod, and copy over the world from the server, and then copy it back after. There is also a MCEdit filter to do the same operation (I think it was linked earlier in the comments here?), but I haven't personally used that, so I can't comment on how that one works.

If you need more help with the mod, I'd suggest we take the conversation to the CurseForge comments of the mod (or some other place like Discord), to not ping everyone else in this issue.

Since this is a symptom of a bigger issue that isn't being fixed, give us an option in server properties to suppress duplicate entity warnings. I've had this error for so long and I've never experienced an in world issue. just the console SPAM so let us turn it off.

There is also a MCEdit filter to do the same operation (I think it was linked earlier in the comments here?), but I haven't personally used that, so I can't comment on how that one works.

Yes it is also linked in the description (changed the link to github directly instead of to the comment linking to github).
But please ask questions about it in r/Mojira or write me a private message.

Can confirm for 1.12-pre6

Confired for 1.12

Always in 1.12

This is probably related to MC-22147, since that bug is about entity duplication, which also duplicates the UUID of that entity. This causes multiple entities with the same UUID to exist in the world.

Confirmed for 1.12.1

The error also exists in version 1.12.2.

Confirm I've run into this as well

[19:46:10] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID 162a9acd-6fc6-46a8-9028-9f0d616dcbfd
[19:46:10] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID af921b4a-b9f4-4084-bae2-374c9d2ad45a
[19:46:10] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID 162a9acd-6fc6-46a8-9028-9f0d616dcbfd
[19:46:10] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID d23b3c39-474a-45b1-8d55-96f5b848d241
[19:46:10] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID e53180bf-8c32-46fc-9262-b4b0d8d12f3f

I've noticed that 3 of my villagers that I have in an "attempted" automated farm, disappear 🙂 One showed back up a few days later, but then recently has vanished again. It is at the edge of my Village, but it seems to be an ongoing thing with me placing villagers in a secure area and they disappearing, sometimes reappearing. Think I've lost 4 now being in this chunk.

And one of my villagers re-appeared today.

[10:00:46] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID af921b4a-b9f4-4084-bae2-374c9d2ad45a
[10:00:48] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID d23b3c39-474a-45b1-8d55-96f5b848d241
[10:00:50] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID af921b4a-b9f4-4084-bae2-374c9d2ad45a
[10:00:51] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID 162a9acd-6fc6-46a8-9028-9f0d616dcbfd
[10:00:51] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID 162a9acd-6fc6-46a8-9028-9f0d616dcbfd
[10:00:53] [Server thread/WARN]: Keeping entity minecraft:villager that already exists with UUID e53180bf-8c32-46fc-9262-b4b0d8d12f3f

Issue confirmed for 1.12.2

My server usually has issues with minecraft:zombie

1.12.2 was already marked as affected...

Confirming for 1.13.1...

This has returned with a venegance on my snapshot server with 18w44a. World created in 1.13 snaps on June 15th and brought through all the snaps except crashy ones. We're getting hundreds upon hundreds of them and the server has become very laggy which of course could be because of this or another reason.

Confirmed for 18w45a and 18w46a. For these latest snapshots, this is related to mob duplication glitch:
https://bugs.mojang.com/browse/MC-138919

Issue still exists in 18w49a, zombie pigman

Does not occur on chunks marked for force loading.

Still on 18w50a and 19w02a and 19w03a

Throwing eggs I can hear an iron golem get hit, but punching and running around–nothing. How is an MCEdit Version 1 plugin supposed to be used on our newer maps??

This issue still exists on 19w03c. Causes intense lag and results in server crashes any time a player teleports to an unloaded chunk

Currently running a server on 19w03c and I'm having a difficult time pin pointing what causes this message to start being spammed.  It appears to have something to do with hostile mobs.  My server runs smoothly during the day time for the most part, but once it becomes night time and someone is out exploring (not in new chunks) the console starts going crazy with the above message or a variation of it with a different entity and the game becomes unplayable forcing us to restart the server.  I was wondering if anyone else has experienced this issue at night time?  

With 1.14 snapshot, it is caused by entities duplicating upon loading chunks, which is related in current open issues [MC-138871], [MC-138919] and [MC-141918].

@Johnibur that makes sense, and would explain the intense lag. This wouldn’t only apply to newely generated chunks correct? Meaning it could happen in any chunk once it is reloaded after being away for some time?

@unknown Exactly. Every time you reload any chunk you might dupe entities again. It's actually an existing game breaking bug since the first 1.14 snapshot that has been ignored so far for some reason, or because it's not clearly stated on the tracker and somehow confused and spread between several issues.

Confirmed happening to us in 19w03c. 

Console is being spammed with the "Keeping entity" line and "Can't keep up" lines.
 

Keeping entity minecraft:item that already exists with UUID 81f33f25-04c4-4fe3-b265-b7e7bfcbd345

Can't keep up! Is the server overloaded? Running 2677ms or 53 ticks behind

Seems to run fine during the day when there are no mobs..

@unknown What you may want to do as a workaround until it's fixed is removing some entities including the duped ones manually. For instance, if you have "keeping entity item" spam, make sure no-one on the server is in searching for a specific item on the ground and then wipe all the registered items on the ground:

/kill @e[type=item]

Note that duped entities are still registered on the global tracked entities list even if the chunks are unloaded. So you may want to frequently hit restart to clean those registers.

Anyone have an update on this issue in the newest snapshot?  19w04a? 

yup, it affects 19w04a too :/ 
It makes the game unplayable for me. I always thought that "vanilla" servers are a lot lighter than Bukkit/Spigot...
4 GB RAM Allocated, Intel i7 4790k, server runs on SSD (520MB/s rw)

It’s crazy, we were running 100+ mods on a 4GB server, with no issues or lag.  Now a vanilla snapshot server can’t run without lag because of this issue... really hope this gets addressed soon as the game is literally unplayable on servers.  

I've had this issue on all the 19w snapshots, started in 18w for me I think. Definitely still on 19w04a. Sadly can't place doors or finish this village :/ I wish the mods would let us leave all of our tickets open so the devs actually see it! This is game breaking and mods have done nothing but suggest an old MCEdit filter that doesn't even work with MCEdit! Mod Neko I @ you because you need to do some research besides shaking this wasp nest of a community trying to answer as many support tickets as you can so quickly. No quality reps on here, just a large quantity of moderators that shut down issues. Haven't you heard of whitespace being free? Let us leave our tickets open, it doesn't cost you anything, and duplicate issues are the only way it gets to the attention of the devs. We do not care if we lose a book from a lectern, we can't even place a lectern in the first place this game is so broken. Rant over.

Duplicate issues are not a good way of getting the attention of the devs. They rely on our volunteer moderation team to collect all the relevant information about an issue in one place, so that they don't have to search through dozens or hundreds of issues themselves trying to find useful information. "Whitespace" isn't free – clutter drowns out important information, and when the devs turn to the bug tracker looking for bugs to fix, they want that information as efficiently as possible, so they don't have to waste time digging through low-quality reports, and can spend as much time as possible improving the game.

This report is about a symptom of multiple other bugs, and is not a bug in and of itself. Given the nature of the issue, these bugs are most likely hiding in some of the deepest, ugliest code in the game. They're fully aware that the whole entity tracking system is awful, and needs to be overhauled or replaced entirely. However, this is a significant and difficult undertaking, and not something that can be done in an afternoon. They have to plan these things out and fit them into the larger schedule.

This issue is still present in 19w05a.

Some background:

I was playing on my server with my friend and we were both in overworld. As soon as I entered the nether portal and spawned in the nether, console started getting spammed with this error (many times per second continuously). I decided to just relog in case it would fix something and... it did.

The strangest part is that the error kept telling about sheep and cows, which are not present in nether, so why relogging in nether (while my friend was still in overworld) would fix something is still unknown.

I am attaching some logs below (the issue starts at line 137).

I am impressed with how many messages were printed in such short period of time.

Edit: I believe that the fact that the console stopped spam for a few seconds after I left might be connected with server freezes whenever a player leaves the game

Can't confirm that. I'm experiencing these messages and the related lags also in the 19w05a overworld. 

While I was alone on the server no messages appeard in both worlds. As soon as several people have played, the errors occured. I've regenrated the world between these two runs 

This seems to also occur when using the nether to travel and going back into the overworld at a different location. The server times out "Tick took 60 seconds, assuming server crashed" and restarts. This continues to happen until the player that traveled returns to the nether.

Noticed when using a Aternos Server using PaperMC 1.13.2

Still present in 19w07a, it generates over 100KB of log data in just 5 minutes. This console spam seems to be happening every time server has a random few-second freeze combined with extreme hard drive usage.

Edit: It seems that there was a specific person that was generating this messages. When two people played on the server withour them, the server worked normally and as soon as they joined (and one other person left) the spam began again. It kept getting worse and worse until the server froze for 60 seconds resulting in watchdog shutdown.

It might have a strong connection with latest issues with server performance described in MC-63590 and MC-138114

Ran into this error with multiple mobs on newest snapshot, took me a while but I found a work around, have everyone log into the server one by one and see who joins last that causes it to throw errors, have that person put their stuff in a chest and then delete their player data and restart the server, you can find their player data through their personal UUID on the server. It shows it when they log in on the console, after deleting the player data restart the server and have them rejoin and port them back to their house, where they retrieve their stuff

Present in 19w08a, new world, after making chunks load (tping back and forth).

I'm having the same issue in 19w08b and I have observed that it happens when a player is near the entities.

I have a villager breeder and on loading the chunk where it is, the messages start to spam on the console. Also sometimes the entities disappear (villagers, cows, wolves, item frames).
I restarted the server several times and logged in at the same chunk, and everytime different entities appeared and disappeared, sometimes duplicated (what lead me to believe that the keeping entity warning is related to causing it to not load properly)

I have a single player world with this "keeping entity" bug.  I'm still using my 19w07a save because of the "ticking entity" bug.  I tried killing everything but me ( kill @e[type=!player] ), then quit out of Minecraft, then relaunched the game, and found that many villagers, 2 iron golums, and a horse were reanimated.  So I killed them with my sword, one at a time.  Again I quit out of the game, then went back in.  And again, the villagers, golums, and horse were back.

The log shows many instances of "keeping entity" warnings.

My understanding is that I need to remove the offending entities with a world editor, but MCEdit is not ready for 1.14 snapshots.

I have created a new issue for this, to record all of my testing and findings. I have a temporary solution for anyone who is interested - but it is quite complex, and requires a lot of time spent removing every single duplicate entity.

https://bugs.mojang.com/browse/MC-145413

I followed Matthew's solution (MC-145413), and it worked!   I no longer have duplicate entity entries in the log, and the places where I could not place a block now accept blocks.  It did take some time to copy UUIDs from the log and paste them into /TP commands, but probably only a couple of hours.  I placed command blocks to kill zombies, villagers, and iron gollums.  It took more than 10 command iterations to kill the last of the duplicate villagers and zombies.

Unfortunately this error occurs on a brand new world, too. So it's more complicated than simply deleting all duplicated entities, because they will be duplicated again and again.
See MC-138871 for more info about our tests.
Regards,
Peter

Peter, I read your bug thread.  I have not had any new duplicated entities since finding and killing all of them.  I'm running single player Minecraft on an older desktop pc (Intel i7-3770, 16 GB RAM, GTX 780Ti, 2560x1440 monitor.  Video settings are towards the slower, fancier end of the spectrum (11x11 blending, 24 chunk render).  My game play is not laggy, so maybe that's why I haven't had entity duplication since killing all the dupes?  I've also stayed out of the Nether because some have proposed that Nether visits cause the light emitting block bug.  Maybe I'd get duplication if I caused my base chunks to unload and reload?

@Jeff, I've never heard that relation between the light error and the Nether. However it can be true, who knows? 🙂
About the dupes: your old PC is far more powerful than my business laptop. 🙂
However in single player I haven't had the problem, only in multiplayer. As @Johnibur found, the quantity of duplication seems to have correlation with the system lags.
However I noticed some duplicated entities in server log some years ago, but never so much, than in the current version.
My opinionis that the solution is not killing the dupes manually, but never create them. 🙂 That's what the developers should fix.
Regards,
Peter

Hello everyone,

Don't know if this helps, but the same keeping entity msg appeared on my server (1.13.2). Never seen it before and it happened today right after I installed and allocated more RAM. It happened for entity firework_rocket right after a server crash, while I was flying through my world.

It's also combined with the 'can't keep up' msg.

Hello everyone,

Don't know if this helps, but the same keeping entity msg appeared on my server (1.13.2). Never seen it before and it happened today right after I installed and allocated more RAM. It happened for entity firework_rocket right after a server crash, while I was flying through my world.

It's also combined with the 'can't keep up' msg.

Definitely still unable to place blocks sometimes in the latest snapshot 19w13a due to this entity invisibility issue.

Confirmed in 19w13b

Confirmed. Got that too, and quite often as well.

Console log produced last time, when somebody was in that chunk:

[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 199a17ca-289b-4991-9746-8a0aa05766b4
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 129de36f-0c73-4ed2-9a65-0b0f051d550a
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1156de39-eb4b-4e39-a296-92df0a6c7e69
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 9582738d-29d1-427e-a6ee-50a5de9f954b
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 43f8091f-49d2-4d5b-b072-ea517f181e34

entered on console, nobody online:

/kill 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/INFO]: No entity was found

Then I join the server, enter this particular chunk, and the server console says again:

[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 199a17ca-289b-4991-9746-8a0aa05766b4
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 129de36f-0c73-4ed2-9a65-0b0f051d550a
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1156de39-eb4b-4e39-a296-92df0a6c7e69
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 9582738d-29d1-427e-a6ee-50a5de9f954b
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 43f8091f-49d2-4d5b-b072-ea517f181e34

Then, again on the console, I try to kill these entities:

/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[Server thread/INFO]: Killed Chicken
/kill 129de36f-0c73-4ed2-9a65-0b0f051d550a
[Server thread/INFO]: Killed Chicken
/kill 1156de39-eb4b-4e39-a296-92df0a6c7e69
[Server thread/INFO]: Killed Chicken
/kill 9582738d-29d1-427e-a6ee-50a5de9f954b
[Server thread/INFO]: Killed Chicken
/kill 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/INFO]: Killed Chicken
/kill 43f8091f-49d2-4d5b-b072-ea517f181e34
[Server thread/INFO]: Killed Chicken

It confirmed, the chickens are no longer.

But shortly after on the console the EXACT SAME UUIDs appear again, but only because the player is still in that chunk:

[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 199a17ca-289b-4991-9746-8a0aa05766b4
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 129de36f-0c73-4ed2-9a65-0b0f051d550a
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1156de39-eb4b-4e39-a296-92df0a6c7e69
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 9582738d-29d1-427e-a6ee-50a5de9f954b
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 43f8091f-49d2-4d5b-b072-ea517f181e34

Wait.. aren't these...?!

On the console still, I try if I can kill it again and again and again....

/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[07:53:17] [Server thread/INFO]: Killed Chicken
/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[07:53:26] [Server thread/INFO]: Killed Chicken
/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[07:53:32] [Server thread/INFO]: Killed Chicken

--> Confirmed... it never dies, perhaps it's undead and we need a /heal command to make it die.. :>

Found a workaround.

You can get rid of these thingies, when you /tp them to your location:

[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 199a17ca-289b-4991-9746-8a0aa05766b4
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 129de36f-0c73-4ed2-9a65-0b0f051d550a
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1156de39-eb4b-4e39-a296-92df0a6c7e69
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 9582738d-29d1-427e-a6ee-50a5de9f954b
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 1848fc94-d4f7-4f44-a17b-d79c284ce194
[Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID 43f8091f-49d2-4d5b-b072-ea517f181e34
/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[09:47:30] [Server thread/INFO]: Killed Chicken
/tp 199a17ca-289b-4991-9746-8a0aa05766b4 His_Cifnes
[09:47:40] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/kill 199a17ca-289b-4991-9746-8a0aa05766b4
[09:48:01] [Server thread/INFO]: No entity was found
/tp 129de36f-0c73-4ed2-9a65-0b0f051d550a His_Cifnes
[09:48:28] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/kill 129de36f-0c73-4ed2-9a65-0b0f051d550a
[09:48:33] [Server thread/INFO]: No entity was found
/tp 1156de39-eb4b-4e39-a296-92df0a6c7e69 His_Cifnes
[09:48:46] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/tp 9582738d-29d1-427e-a6ee-50a5de9f954b His_Cifnes
[09:49:02] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/tp 1848fc94-d4f7-4f44-a17b-d79c284ce194 His_Cifnes
[09:49:13] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/tp 43f8091f-49d2-4d5b-b072-ea517f181e34 His_Cifnes
[09:49:21] [Server thread/INFO]: Teleported Chicken to His_Cifnes
/kill 43f8091f-49d2-4d5b-b072-ea517f181e34
[09:49:30] [Server thread/INFO]: No entity was found

No worries.. the chicken never arrived on my locations... so when you have a bugging Zombie, it will not attack you, after /tp. : )

As consequence... the duplicate ID log has never shown up again since /tp. --> works for me..

This warning message still happens on some occasions when visiting remote chunks on 1.14 and 1.14.1-pre1. But the message is no longer persistent. It tends to disappear on next visit.

Can confirm for Minecraft 1.14.1.

Johnibur, try /TPing this entity to your position, as I wrote.

Case solved.

It's not about the duplicate entities, those do not appear anymore. But this warning message persists in 1.14.1. Appearing on new generated chunks too. Not always consistent, but often you get this message after a relog.
So this ticket is for this warning only.

On 1.14.1, MC-150170 was causing these warnings, but was fixed in 1.14.2-pre-1. I haven't seen this warning since then.

Does anyone still see these warnings in 1.14.2?

Still see this in 1.14.2 every once and a while, but it's pretty rare.

Had this happen in 1.14.4 the chunks may have not been loaded since a previous version of the server had been run (when this was a known and unresolved issue).

The console was spammed until the user logged off. 

If I have time I'll attempt the MCedit fix.

Affects 1.15.2. Scanning my logs, I still get these warnings every once in a while, but they're incredibly rare. Haven't got them in 20w06a or 20w07a.

Is anybody still experiencing this?

I haven't seen this happen in a game-crashing sense for about a year now. Still happens occasionally but not on that scale and not enough for it to feel like a bug.

I currently have this bug on a server I am running. 

Since 1.16.2 i no longer see this issue myself

I haven't especially paid attention to this in a while because duplicated entities haven't been a problem for me in quite some time now. The "message spam" wasn't really a problem, it was that entities would get duplicated and only one of them would be "active" during any given game session, which caused a myriad of problems. From my own personal experience, it would seem that this bug is fixed now.

Still experiencing that on 1.16.4 server (with some datapacks from vanillatweaks, though not even using armor stands one, so I don't think they are the issue). It's not spam per se, but it happens every once in a while if someone places armor stand. Not sure if it's making anything more, as I'm not the one who creates them.

Comfirmed on Paper 1.17.1.

[Mon, 20. Sep 2021 17:36:43 CST INFO] x56465163/111.242.180.4:58230 logged in with entity id 210350 at ([world]2193.300000011921, 106.0, -9605.827075037218) [Mon, 20. Sep 2021 17:36:43 CST WARN] UUID of added entity already exists: EntityCat['Cat'/210394, uuid='ff7800a8-3758-43fa-90d0-a824d68103b0', l='ServerLevel[world]', x=2166.00, y=80.00, z=-9627.12, cpos=[135, -602], tl=820336, v=false, rR=null] [Mon, 20. Sep 2021 17:36:43 CST WARN] UUID of added entity already exists: EntityCow['Cow'/210408, uuid='3f37a192-7198-48d5-9696-363b951b94ff', l='ServerLevel[world]', x=2199.98, y=78.00, z=-9651.55, cpos=[137, -604], tl=1705855, v=false, rR=null] [Mon, 20. Sep 2021 17:36:43 CST WARN] UUID of added entity already exists: EntityCow['Cow'/210410, uuid='fe2396a3-baba-4f95-b6ad-5fd915b57f32', l='ServerLevel[world]', x=2203.76, y=78.00, z=-9651.51, cpos=[137, -604], tl=1691902, v=false, rR=null] [Mon, 20. Sep 2021 17:36:43 CST WARN] UUID of added entity already exists: EntityCow['Cow'/210412, uuid='4d754e60-8346-4230-ac7b-ca39039747da', l='ServerLevel[world]', x=2200.81, y=78.00, z=-9650.88, cpos=[137, -604], tl=1692674, v=false, rR=null] [Mon, 20. Sep 2021 17:36:43 CST WARN] UUID of added entity already exists: EntityChicken['Chicken'/210462, uuid='be29e53b-1e52-4467-90f3-6bb76573036a', l='ServerLevel[world]', x=2336.03, y=80.00, z=-9625.47, cpos=[146, -602], tl=250518, v=false, rR=null]

Mojang does not develop Paper. Only comment if you are able to repro with the official server jar.

Does this still occur in the latest version of the game?