I think the sheeps bugging out of fences, because they want to eat fresh grass. All my sheeps in the farm standing always near the fence, when thy make the area to dirt.

I often found sheeps outside the fence and sometimes I see how they bugging out

Steps to Reproduce:
1. Build a sheep farm
2. Spawn/Farm maaaany sheeps
3. Let they eat the grass
4. See how they want to go outside the fence and sometimes bugging out.