Recently I have been trying to complete of all the Halo: Reach achievements in the MCC. Currently I am focusing on getting all of the legendary achievements for the single player campaign, however despite the fact that I have completed all of the levels on legendary difficulty, I have not received the achievement for the completion. On my service record it states that I have completed every level on legendary, except the level Exodus, which I have replayed numerous times in order to attempt to complete it on legendary, but nothing has changed. Any ideas on how to fix this would be greatly appreciated.