It's the Xbox gamer's worst nightmare -- you do everything that you need to pop an achievement but you didn't get the "achievement unlocked" pop-up. When you check the progress on your console, it says it's "".We've heard stories of achievements in this state (or stuck at 100% completion) for up to six months before finally popping. This is an annoyance at best, but at worst it could cost you your place in a contest such as The Ultimate Head to Head Contest 2 We have some good news for you -- the Xbox support thread on this issue has been updated to read:

If you were connected to Xbox Live and you completed the full requirements for the achievement but the achievement seems ‘stuck’ at 100% complete or “Done! Unlocking…”, go to the achievement detail view on Xbox.com or on your Xbox One console to double-check whether it is still locked.

To make things easier for you, we've added a new panel to the Xbox One achievement pages:This includes a link to the appropriate page on Xbox.com. Simply log in to your Xbox account (if needed) and itforce the stuck achievement through the system.