This has been happening for awhile now, but for some reason sometimes an entity will act strange. This can be with anything--I've seen it with mobs, item frames, and paintings. The entities don't get "recognised" by the player, and they can't be hit or interacted with. This appears to happen randomly, and with hostile mobs too, making this extremely annoying. I'm playing on my survival world, and I have villagers. When I leave my house, unload the chunk, then come back, sometimes I can't trade with a few. When I relog it fixes this, but it just happens again and again. You can hit them with projectiles though... You just can't punch them or interact with them. It seems random with hostile mobs, one will occasionally do this. You can imagine the sheer annoyance when it's a creeper...