I first discovered this bug while developing a mod using the Fabric platform and first thought it was an issue with Fabric and not Minecraft. My console would log a couple "Bytes Mismatch" errors, but one time there were so many the game was forced to crash. In order to try to find the issue I stopped the mod from loading so I thought it was a Fabric issue not a mod issue. So just to confirm it was an issue with Fabric I tested it in the vanilla snapshot and the same issue occurred. So that it why I'm confident although the crash only happened in a modded situation that the same errors I am experiencing are being felt in the vanilla game and not as a result of any modded client. With that being said the follow is the log and the crash report from the crash (Which was in a modded environment) and my success at getting the same issue to appear in the vanilla game. The first two files is the crash log and console log of the crash in the modded environment, the third file is a log from the vanilla game.
The crash log states that the trace of the issue is that "Backend library: LWJGL version 3.2.1 build 12 Backend API: ~ERROR~ IllegalStateException: Rendersystem called from wrong thread"
Given my very basic knowledge of the game, this makes me guess the issue is that somewhere in the new implementation of the blaze3d rendering system, something is calling the LWGJL thread locked process from another thread.
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please create a new ticket.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run modified server software.
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