From what I've seen, cows occasionally can't jump in water when besides walls. I tried to make a small cow farm and occasionally when the block the cows were standing on occupied with water, they wouldn't jump, even though they jumped previously.

It seemed to trigger when they spread out (spawned the cows in with eggs and they were all within each other, touching them causes them to one spread out).

This seems like it could just be a change in AI for cows or general gameplay, but they seem to be fine when replacing the walls with glass, so maybe walls have a specific property that makes cows behave different (even though last I knew cows always jumped in water).

I saw other bug reports that looked similar to this one but all were resolved, so I'm making this because if this bug is the same as the others the problem isn't resolved yet.