The Slithering Dead can't progress

I reached the end of the Venom Crypts and the quest is stuck on "Explore the Venom Crypts." I reset the instance just to double check, and it still won't progress.

Specifically this is the cruel difficulty version of the quest.

EDIT: I'm an idiot, the minimap icon threw me off. I was finding the sarcophagus room (which has an icon as if it were a point of interest even though it isn't?) and not the one with the corpse for the venom. Oops.