MC 1.12.2
ImprovedMobs 1.2.2
Sudden server crash (for two people).
Crash report - https://gist.github.com/kellixon/4b00be1339a74df0d9cdca069cfaa8c6

can you go to this location here (64,64,600) and tell me what tile entity is at that position? the only reason that crash could happen was cause a the tile entitys size was wrong and that might be an issue with another mod