There is a recurring bug where ladder games sometimes don’t register as finished. In your case:
This game: Ladder Challenge: isor(#100) vs Osborn12(#71) with Osborn12 has failed to close with respect to ladder details, preventing a third challenge by you.
See also: Ladder game stuck after timeout
Note: It may take a few days to get it sorted once a mod passes it on. I have invited AdamR to the thread as he dealt with the previous occurrence.