Playing on Dwarven with permadeath. I have walked through a good section of the dungeon, and not a single MOB has spawned. I could see a room or two, but this is silly! I'm going to copy this save, then try to load the autosave to see if maybe I can get it to generate right. xD
Reloading the autosave worked. I still have the corrupted save, in case you'd like to examine it. Bizarre bug!
I had something similar happen on my game when I went down to level 9. The enemies seemed very sparsely populated. I think I ran into maybe 10 fights the whole level, and a zoo, same mode settings.