Every time I open the game, I have to restart at the first map. My characters and items save but not the gaming levels themselves. I can play level 2 if I do it right after beating level 1, but if I close the game only the level 1 map is available. Is there a way to fix this?
Found a fix here, on the official forums.
Right click on the game in steam -> Properties -> Verify game cache When I did that it said "2 files failed to validate and will be reaquired"
Then I restarted my game and got all my progress back. I never had the problem with deleted characters or lost items though. I was just unable to access levels I had unlocked. It might be a steam updating problem.