Mobs fall through blocks and die on spawn

I've had a very strange issue where a few of my mobs just fall through the floor and die. only a few of my mobs actually work and they're the simple ones. It seems to be an issue with disguises but I have both updated versions of Mythic mobs and libsdisguises. I even have the updated version of protocollib. Anyone know a fix?

(Update: after trying to replicate the "falling through the floor and dying" part. I realized that after updating to the latest version, the mob just doesn't spawn at...

Mobs fall through blocks and die on spawn