Opponent resigns so I continue with bots. Opponent had 6 coffers at the time.
Lord Rat plays Swashbuckler, draws three cards, +1 coffers so now has 7 coffers, then freezes. I think it's frozen on the prompt for "spend coffers to avoid getting the treasure chest?"
Game #99599447
Yes, that would be my guess as well. I've put this on an internal bug list.