It happened to me about 10 times in the last month. Never before that and I have been playing since November. Ubisoft told me to turn off cloud sync in uplay options to prevent future issues. They also told me to get gamesave-manager. You can just click once to back up your save and I think you can set it up to auto save your game once a day/week/month. Its been 4 days and haven't lost my save yet. So not sure if the gamesave-manager will work nicely yet or not. Since I have started over so many times lately I observed if I play only stuff I can get 100% on for the first few songs then it will level up all songs. If I start with things I can't play well it ends up taking forever and all songs seem to go up about 10% for each play no matter how well I know them.