If there are more than 2 cows in the space of a single block, I am only able to breed one of them. They then all face me (because of the wheat in my hand) and I'm unable to breed any more. This is still the case even if I displace them by walking into them. With F3 + B pressed it looks as if all the cows' hitboxes are sharing the exact same place. I think this is why I can't breed them.