@Maxell_Rus I'm just busy playing through the Omega DLC, also on PC (I noticed your comment about being on PC in another thread), but in my case the achievement unlocked just fine. Do you still have a save file from before you discovered the identity of the Talons leader? If so you can try just playing through that section and see if it unlocks the second time around. Make sure you have no internet connectivity issues too, since the game needs to communicate with EA servers in order to unlock the achievement on your profile. Another thing I sometimes notice with achievements are that they do unlock but don't show up on your profile as soon as you exit the game, or even if you check the Achievements page from the Origin In-Game overlay. In this case they've always appeared after I reload the page from the Origin menu in the client.
