I sent more and more and more messages about the achievements for this game.
ACR was the first game with it in UPlay, after there were FarCry 3 and AC3.
Actually, AC3 and FC3 save offline the achievements unlocked by the player in a file named *.spool (40.spool) and this file is uploaded too to the Ubi's server. If you install UPlay on an other PC and connect to your account, when you visit the game's page on UPlay, the *.spool file for this game is downloaded automatically.
But, for Assassin's Creed Revelations, it's not the case. The .spool file is not uploaded/downloaded so when i re-installed my system, i forgot to save on my USB Key the ACR spool file. Result = i lost all achievements unlocked...
So please Ubisoft, i already sent more message to the technical support without good answer. Create a patch for UPlay to upload/download this *swear word removed* ACR spool file.