A growing number of LittleBigPlanet players are reporting that the game suffers from a terrible glitch that deletes game progress as well as custom contents randomly.
"I've completed all five acts, and when I turned off the power and played again, all that was unlocked was Act 1-3. However, my scores from Act 4 and 5 were still in place-- it's just that I need to unlock them all over again as well as collect the prize bubbles," SuperPhillip posted on the game's official forum. "To add to it, the saved costumes I had of the Metal Gear crew were missing from my saved costumes folder. Though the actual parts to create those costumes are still there thankfully."
Other users reported losing lots of user-created contents. "I lost four costumes and she lost all 12 of her saved costumes, as well as losing the level status. Also we found that all of our community and saved photos were erased too," says justsayno2girls.
There is no solid explanation for the bug yet, but most players believe that it happens once the user profile passes a certain size limit. Media Molecule still hasn't addressed the issue yet and, considering it's the holiday season right now, they are not expected to patch it in the next few days.