Invincible and Invisible Monsters

Encountered some mobs being invisible only noticeable by sound, shadow, and the damage they deal. So far this only affects small fodder mobs like zombies and skeletons. Attempts to attack them dont work. Melee, range, explosives via arrows and tnt, and traps such as the red tower trap floor. Only way to counter this is to constantly move around to have all the mobs regularly within sight which is tedious. I have had to reset to checkpoint multiple times to pass one floor. Please fix this.