Act V: Kitava Not Spawning

Just as the title says: I'm in Act V and I have the quest "The Ravenous God" with the quest text "Use the Sign of Purity to defeat Kitava", I have the Sign of Purity in my bags, and Kitava will simply not spawn at the Cathedral Apex. I have reloaded the game on a couple of occasions with no change - I am able to zone into the Cathedral Apex and nothing happens at all. Suggestions?

Did you click on the altar in the Apex to put the sign of purity in it?