So during act 1 when you first enter the caves, I've came across some bats that become invulnerable. They start off in a pack of around 10 and then there is like 3 of them that won't take any damage after I kill the rest of them. They end of following me around the rest of the level dealing minimal damage but it stops me from leveling and even equipping new gear I pick up. I got to the second part of the caves and had the same thing happen. A few bats became invulnerable and followed me the entire time. If it matters, I'm playing a range character with a bow