there was a creeper in my house, stuck in its place, it was on the other side of the house so i shot it with a bow and the arrow went straight through it. i ignored it and went to the left side then the creeper blow up animation started to the creeper and it blew on the otherside. i think what is happening here is that the textures and the models of the mobs get stuck in place, and their hitboxes keep going (that makes them invisible).