There seems to be a bug where if you have go to confront Xaven during Fortress of Solitude, you can start the Hell to Pay portal. It's probably because I had the item from the Stranger Things quest because of New Game+. You're able to return to the fortress and beat feat after finishing Hell to Pay, but the fortress is already looted (If you did before) with all the enemies respawned, and when you get to the portal room you find that all your party members are there like when you are doing the ritual, with the Borgen in the center of the circle like he should be.
Just a suggestion, but maybe make there be something to do with the weapon upgrade parts during a New Game+. Having duplicates of every upgrade item is a bit annoying, and clutters your inventory a lot.