Stack overflow - Server wold files unable to load now. [minecraft/ChunkSerializer]: An Entity type null has thrown an exception trying to write state. It will not persist. Report this to the mod author java.lang.NullPointerException: null

https://gist.github.com/ProsperCraft/44cc105dc8420a919ca2862d00cdd229

We were playing along with tons of mobs around us, then suddenly we got kicked with a stack overflow message(sorry I didn't screenshot it, it isn't in the logs) and they server saved and just sat there, loading the world gives this same message then stops, not exiting.

Crash log - https://gist.github.com/ProsperCraft/a512cf3dd28e2713e1156d09a4185773