Hi! I have a modpack of 180~ mods and the bug is about a strange spawn of mobs underground (i think is only underground) i dont know why no mob spawns in caves until a time but instead of spawning some it spawns A LOT around 2500 entities and i tried deleting or moving the rubidium mod out of the mods folder (because is not crashing) and the bug seems to solve. I'm attaching my mod list just in case:
listofmods.txt

I resolved was not a bug in this mod