At the end of a Domination game at Yemen, I received some "UI Error" and ended up resetting me to the beginning of the night. I LOST levels, going from Prestige 3 Level 36 to Prestige 3 Level 30. I also lost my weapon attachment unlocks and headshots. Everything I earned that night just vanished. However, I have proof via the Call of Duty Elite Website and the theater mode that I WAS a level 36 and that I lost my attachments.
Hopefully somebody from Treyarch sees this so that I can a) get my XP and challenges back and b) fix this glitch so it doesn't happen to anybody else.