Same problem, it seems to randomly appear at some point in the game.
I tried turning off my mods, but it didn't help either. Would be nice to get a short hotfix telling us which line in the save we'd have to change to make it work again.
Note: This was a completely new game, and it DID work at first. My guess is that either some of the classes or skills might be buggy.
It also still works with Quests that give you the normal menu with the plus sign, for example right before the Siege