I was (/am) also having this problem, so it was reassuring to see I’m not alone.
Looking at it, I think it’s because something changed in the way lesson results are submitted.
I don’t have a full solution, but a workaround is to add: https://www.wanikani.com/lesson/* to the “User excludes” in the TamperMonkey Dashboard > WaniKani Katakana Madness > Settings page:
That’ll keep that katakana madness in the reviews, but stop the lesson quiz from restarting.