It looks like it was lag.
I just finished my 3rd win, and when coming out of that game, it said Quest completed, and it now showed the correct 3/3 wins.
In this game I made sure to choose a different opponent. I don't know if that affected it, or if an Admin saw my post, checked my results and corrected it. But whatever it was, it's now correct.
(I considered deleting my original post, but decided to leave it up, just in case there is some subtle internal error, that others who are playing repeatedly against the same opponent run into also. I just usually grab Verboten unless we are instructed to find different opponents.)