When it comes to Achievements, Microsoft giveth and Microsoft taketh
away, as a large number of users have woken up to find their profile
wiped clean. Microsoft is aware of the glitch and is working to fix it,
but in the meantime affected Xbox gamers are instructed to delete and recover their profiles in order to recover their video gaming history.
Despite the vocal response from customers, the problem does not seem to be massively widespread, no doubt making the job
of identifying the cause that much more difficult. ”Turned on my Xbox
this morning and booted Mass Effect 2. Got an Achievement, hit the Guide
button to check out what. And then I discovered that my Gamerscore had
been reset to zero,” wrote a Eurogamer reader.
Source Eurogamer