Angry and exasperated gamers have filled a thread on Ubisoft’s official forums for Assassin’s Creed III with complaints that the first downloadable content has erased their game progess.
Assassin’s Creed III: The Hidden Secrets is available for download now for players who have purchased the Season Pass, but everyone should probably hold off unless you want to risk this game-breaking bug.
According to some of the posters, after installing The Hidden Secrets, the game reset their money and main mission progress back to zero. Oddly, the side missions are unaffected, as were many other features.
This bug isn’t affecting most players, and those that are having issues seem to only be on the Xbox 360. We have contacted Ubisoft to determine who is at risk and what it is doing to address this problem.
In the meantime, the DLC will likely remain on the Xbox Live Marketplace for others to download until the publisher can dispatch a new update.
Source: Xbox 360 Achievements