I've had two of games where I've gotten to the last floor and it bugs out. Both times I had less than 4 cards remaining, which I suspect may have something to do with it. Also, I don't think the XP counter goes above 52, which I'm not sure is related or not.
What happens is that I get to the last floor, I click a card and it flips, but the effects don't process, and it doesn't say I've completed the dungeon afterwards.
The first time I got to the last floor with one monster card remaining (which should have killed me), flipped it, took no damage and didn't die.
The second time, I got the last floor with the last Donsol and a potion card with enough shield and health to win if I drank the potion first. But flipping the cards did not trigger the potion or the damage and the win condition didn't trigger either.