MuMe

Glass held by an armorstand also triggers this. I made these balloons with invisible armorstands holding glass, all entities/signs/chests/normal glass render in front of the glass. Yellow glass does this more clearly then red glass.

Glass behind campfire smoke in 1.14 also gives this bug.

Don't think the client logs tell anything about this. In this log I did this:

1. Started 1.14

2. Went into Realms world 2

3. Downloaded my working map with datapacks from the Realms backups

4. Switched to world 3

5. Uploaded the map I just downloaded

6. Got the (500) error message

7. Closed the game

[12:09:26] [Client thread/INFO]: Setting user: MuMe
[12:09:29] [Client thread/WARN]: Skipping bad option: lastServer:
[12:09:29] [Client thread/INFO]: LWJGL Version: 3.2.1 build 12
[12:09:33] [Client thread/INFO]: Narrator library for x64 successfully loaded
[12:09:33] [Client thread/INFO]: Built for minecraft version 1.14
[12:09:53] [Client thread/INFO]: OpenAL initialized.
[12:09:53] [Client thread/INFO]: Sound engine started
[12:09:53] [Client thread/INFO]: Created: 1024x512 textures-atlas
[12:09:53] [Client thread/INFO]: Created: 256x256 textures/particle-atlas
[12:09:53] [Client thread/INFO]: Created: 256x256 textures/painting-atlas
[12:09:53] [Client thread/INFO]: Created: 256x128 textures/mob_effect-atlas
[12:09:58] [Client thread/INFO]: Built for minecraft version 1.14
[12:09:58] [Client thread/INFO]: Realms library version == 1.14.13
[12:09:58] MCO Compatability Checker #1/INFO: Realms is available for this user
[12:16:42] [Client thread/INFO]: Stopping!

And checked the downloaded world. The datapacks zips became folders again.

Thanks Jakob!
I see whats going on now.
When you download a world from your Realms backups it changes the datapacks from zips to folders. So we uploaded usable datapack zips, but when we download the worlds we get datapack folders instead.

So this bug consists of 2 things.
-A totally non-descriptive (500) error message. It should have said something about unrecognizable datapacks.
-A bug in downloading backup worlds. When we download backups from Realms it makes our datapacks unusable for re-upload to Realms.

Brian Ronald
Sadly disabling vsync doesn't do anything to fix this problem.
You sure you had the exact same problem? You can check with mod violines instructions to see if your bug was the same.

Everyone on my realms server confirmed that they have this problem in singleplayer and on the server.

Datapacks are the problem. Doesnt matter which datapack I have, the datapacks are the reason for the failure. Removing all of them fixes this problem.
My server uses datapacks a lot for quality of life and extras to make my server unique and fun. It's a huge blow to my server now that I can't use any of them. But at least I can play again.

Duplicate MC-149127 also talks about datapacks.

Got this problem in old worlds and new 1.14 worlds. A friend of mine reported me the same. World generation just doesn't keep up at all when flying in creative.

Pre-release 5 of 1.14 did manage to keeps up, didn't have these problems there. The pre-release is more playable then the release. But I mainly play on realms so I have no choice but to play the latest release version.

Got the same problem with my 1.13.2 world now 1.14 has come.
With the full version of the map and an older backup I get the (-1) error.
With a version where I deleted all far away region files to find new villages/biomechanges, I get the (500) error.

My world uses multiple datapacks/commandblocks/gamerule changes.
Tried the optimize for 1.14 function, with and without deleting cashed data. But nothing changed.
I can open the world in singleplayer 1.14 but the world loads extremely slow.
I can send the world if needed.

If I don't delete POI data I cannot play at all, as it crashes right after starting the world.
But my only reason to do this is to check for bugs with my Realms server before the full release. My Server uses multiple command systems and datapacks, so I need to test those before the server breaks after the automatic update of realms. As long as i delete POI data I can at least test the other things.

I have a 1.13.2 realm map that I opened in 1.14 prerelease 1. I believe this is at the edge of the transition from 1.13.2 -> 1.14 world, but not 100% sure that this is the edge. I converted the world to a 1.14 prerelease world before opening.

See:

Villagers(NPC) are not the problem, new 1.14 villages(location) are. Problem still occurs when you kill all NPCs
Did not have this problem with 1.13.2 villages, but a newly generated village is a problem.
When you delete the POI files you can play again, until you find a 1.14 village, then close your world and try to rejoin.
POI likely stands for Points of Interest, villages are a point of interest. A Pillager Outpost is likely aso a Point of Interest, but no crash at those locations.

Hope this helps.

Affect me in 18w19b, wanted to test new features, but I quickly encountered this bug.
First time it triggered right after I picked elytra from the creative menu and tried to fly. I am unable to return to that world.
So I made a second world with a different seed, everything seemed fine, but when i wanted to teleport to 1000, 100, 1000 it happened again, making me unable to return to both worlds.

1st world:

2nd world:

I loaded my world that has a jungle at spawn in 18w11a to test my builds with the new stuff.
Before I knew it the whole jungle went up in flames from 3 different locations, even rain had a hard time putting out the fire.
Its a multiplayer world that had been running a few days in 1.12.2 and this never happened before.
This has to be fixed or else I need to disable firetick with the update... But that would be lame.

Thanks for your response.

Because of your response I retried. It seems breaking the old spawners and placing new ones fixed the problem.
Had the spawners premade in 1.12.2 with zombies as placeholders. Putting drowned in the original spawners make them not work. But it works fine with new spawners.

I am happy because that makes my temple possible.