Once I removed Epic Fight everything worked as normal and spawned mobs again.
crash-2021-04-21_14.03.26-server.txt

Try downgrading EpicFightMod version by
version till you find a lower version that works.

I have the same issue, oddly enough it only seems to have applied to the spawners from when dungeons arise and not a different dungeon mod I have installed.

It's definitely the result of the spawners becoming ticking entities once they actually start spawning. Flying up to one in spectator wont result in a crash, but the moment I pop into creative or survival the game goes down.

I have the same issue, oddly enough it only seems to have applied to the spawners from when dungeons arise and not a different dungeon mod I have installed.

It's definitely the result of the spawners becoming ticking entities once they actually start spawning. Flying up to one in spectator wont result in a crash, but the moment I pop into creative or survival the game goes down.

As I said, try downgrading till you find a version that works.