Animals Glitching through enclosed area and roaming free

I have a few farms with double high fencing due to the animals sometimes jumping over each other, but they still manage to glitch through solid blocks.

My cow breeding/farm contraption encloses baby cows in a 1 wide, enclosed space to hold them and when fully grown or still baby stage, they glitch out completely and roam the breeder cow holding pen, at least 10 of 25 cows I have witnesses move through the solid block and glass block, and then roam around. At first I thought it was a graphic glitch and they would be retracted back in but, no, they actually become real entities after glitching out of the holding chamber.

Not sure if this is a bug, or just happens due to the number of entities.

Any suggestions would be great.

Couldn't take screen shot due to the farm not in operation at the moment,