Yesterday, D3 Publisher rolled out a new update for Marvel Puzzle Quest. With update R77 comes brand new four-star character Carnage and a few fixes that are, unfortunately, being overshadows by a massive game-breaking bug.
According to users on the game's forums (and D3 has also confirmed it), the new bug causes the game to crash in the middle of a match. Not only do you lose any progress, but it also counts as a loss/quit, meaning your characters still take damage.
At this point, it appears the bug is only affected iPhone users, but D3 is looking into the problem. The developer has created a separate forum thread where you can report any issues your encountering.
Hopefully the issue gets fixed sooner rather than later. If not, maybe we'll get some sort of compensation.