mobs are clipping through walls and suffocate

What I expected to happen was...
the mobs to stay put and unharmed when in a confined spaces surrounded by other mobs

What actually happened was...:
i keep farms of large amounts of mobs in confined spaces and when i leave the area, unloading it, then returning i occasionally hear the mobs suffocating inside the walls they are contained by. they occasionally also just pass right through the block. i have only ever observed this in the version 1.10.2

Steps to Reproduce:
1. put a relatively large amount of mobs in a confined space.
2.unload the chunks and reload them by using portals or leaving the area
3.observe mobs suffocating in the walls