Fences 'Leaky' for animals in 1.10.2 for PCs

Fences appear to be 'leaking' animals. Chickens, sheep, cows, etc are found outside of their fences seemingly at random. Have not witnessed such a leak, but leave the chunk regularly and return with a few escaped animals – but not all and not the majority. Thought it might be a reproductive crowding issue, but have now witnessed it in animals I haven't been breeding, either. (Have not seen this issue with any prior versions of Minecraft.)