I'm running a private server with a custom modpack, and the server crashes at frequent (every few minutes) yet seemingly random intervals whenever a player is walking around in the Nether.

These crashes do not occur in singleplayer. They also seem to only happen when players are actively moving around in the Nether, loading new chunks.

Looking at the logs and crash reports, it seems to be something with MultiMob, but I can't make sense of the cause.

Relevant section of the log:
https://pastebin.com/zJmkkYeT

Crash report:
https://pastebin.com/QPX29D5y