I've noticed that quite often mobs will freeze and nothing will move them. The strange thing is that it does not affect all the mobs in said world. It's not that certain mobs dont get affected, it's that only certain areas in the world will freeze up. Only the mobs are affected. The only way I've fixed this issue is to go off the game and go back on, but quite often the frozen mobs will despawn. I haven't seen this bug before. It has been active for a few days now.