Marc Swenson

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

Case solved.

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..

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.. :>