does mod affect mob spawn?

it feel realy weird, had a few days in a row not seeing any hostile mobs.
was inside a cliff base, but was looking for mobs time to time and there were none. at least expected zombies to try to break in

**does mod changes mob spawn/despawn logic?
what exactly mod does?**

please, consider adding changelogs

(over all my fps is like ~1.5-2.5 times bigger time to time, so ig mod does its thing)