I have no idea - maybe some world generation settings
Or check the level.dat for the seed
Copy the seed, create a new world with the same settings and the seed
Then copy level.dat, level.dat_old and session lock from the new world to the broken one
Delete the new world and test the old world again
There is an issue with an entry in your level.dat
java.lang.RuntimeException: Tried to read NBT tag with too high complexity, depth > 512
Maybe check this file with an NBT editor
Remove crackerslib and the mods requiring it from your server (Mob Battle Music, Story Mod and Cracker's Wither Storm Mod) - these are client-side-only mods