After i kill the npc's sometimes they go through the floor. If i kill them in werewolf form they do the same thing. I wanted to see if anyone else had this problem.

Yep! at various times and places that seems to be happening more and more. Creatures, animals and people have been "disappearing" from my screen when killed. At different times I have found said NPC on a lower level. Don't always find them but sometimes I'm not even looking anymore.

Yes had this many times myself. Mostly happens in caves and such, open spaces seem to fare better with it only happening very rarely.