...the Chasm of the Dead, mostly if not exclusively (IIRC - this was some time ago) in the area where you find the Lich instructions. What used to happen was I'd be fighting (say) 4 of these things, moving around in melée combat. I'd kill them and move back a bit to wait for their reincarnation, and only 3 of them would return. There was no rhyme or reason about it that I could identify, and I don't think it was consistent.I don't know what happens if by chance you are standing on the spot where one of these wants to resurrect itself. Could that be it?