Guacamelee! Super Turbo Championship Edition

Just putting this in here because it happened with this achievement. I was playing co-op and defeated Flame Face but the achievement did not unlock so I thought you must fight him again. My friend left after this so I continued on solo.

About an hour later I killed the Chupacabra using only slam but that achievement didn't unlock. I went back to the main menu and noticed that my gamertag was not in the top left where it should be. So I signed in and reloaded my game and I was back at the checkpoint just before I fought Flame Face again, defeated him, and the achievement unlocked.

I don't know if this is related to co-op but just in case it is, when your co-op partner leaves the game go to the main menu and make sure you are signed in otherwise you could lose a lot of game play. Lucky it was only an hour for me.