Update #2. I went back to a save a little earlier, though still in the same area of the fade. Did a few of those small skill points side quests, then fought the Aspect of the Nightmare again. This time, when that spider (Darkness) showed up, I made sure he was dead before killing the boss and that seems to have worked. The game advanced and the cutscene cued as it should.
Hope this helps for patching or anyone else experiencing this bug, because fighting a boss three times to move forward is not fun.
Thank you for posting your experience and your solution. I was playing through and encountered exactly the same problem twice. Clearing the spider first worked for me!
