The rotation of mob/facing coordinate (only the first value) doesn't match every time with the values of Rotation from the data command. These values aren't actualizing every time sometimes they freeze but the entity rotates. I've tested this on zombie, cow, horse, llama, wolf.
In the example, I've used a command block to tp the armor stand where the cow is watching. I'm not totally sure it's a bug but it's not practical for custom entities.