Not sure how this doesn't have a forum yet, but if you Chono mentor and then unmentor, you cannot use Ascension spells until you exit the game and come back in.
If it helps, zoning works for me (the main potency spell was greyed out until I zoned, then I was able to cast it again). (Disclaimer: Haven't tested it after today's update, though, so ignore if this just started today.)
