I'm not sure about the first captive, the last boss won't appear until you pick up the Husk(which is found right behind pre-last boss, the melee guy located in a room after Spawn of Mephala) and talk to the guy near the dungeon entrance again. I'm not sure if the quest bugging out at the captive stage could prevent you from picking the husk and interacting with that npc though. Drop the quest and try it again? I'm on PC but that's the usual solution for most bugged quests.