Invisible Zombies

When I'm playing in a friend's Realm, sometimes there's invisible zombies that fight me, but I cannot see them and cannot seem to fight back and sometimes I die and I know this because I get the death message that I've been slain by zombies. There are a few times I found frozen zombies standing around nearby when this happens and I cannot seem to fight them, my sword just slices through them like they were air. One time I found a cow like this too, just couldn't do anything with it. Hope this gets resolved! And still waiting to purchase my own Realms when they fix it for the PS4!