The game sometimes crashes randomly giving this error message.
This error occured for Version 21w43a & Pre 7, with no indications on how to reproduce it.
I will upgrade the server the world is running on soon and give feedback if the crash still occours.

A noticable problem is a certain chunk (will make a bug report of that too soon), maybe that has something to do with it.
Crossing the chunks borders in a positive X direction or a negative Z direction results in a short freeze, only reproducable on the server and not in the same world being played singleplayer. Only the person crossing is affected by the freeze.
While the game crashes, the chunk has always been close by.

Id gladly answer any questions.