The lights are on
A number of users are reporting that after downloading the latest Assassin's Creed III content, Hidden Secrets Pack, that the game has erased mission progress and reset other stats.
Ubisoft was quick to respond with the issue, saying on its forums, "Just a quick heads up, we're able to reproduce this issue at the studio and are working on a fix/workaround. From what we can tell, this problem seems to be rare and should generally only affect a very small number of players. That said, we're taking the speedy and complete resolution of this very seriously."
The publisher then offered tips on avoiding the bug. "Do not load your saved AC3 game while the DLC is downloading in the background. This appears to be the key trigger for this bug. You can do anything else you want to do, just don't load up your saved game and play it while the DLC is downloading."
[Source: Ubisoft forums]