I’ve just started my solo legendary playthrough of Halo 4, and after completing the second mission, some coop achievements unlocked. At first, I thought there may have been something wrong with those achievements because when I checked my missions it said I had completed it solo. However, after completing 3 of the missions, I checked the campaign leader board and realized that it says that 2 of them were in coop. For some reason, the game counts you as a second player when you quit and resume a mission. Hopefully, it will be fixed soon and those missions will be recognized as solo like they should be. Hope I don’t have to do them again. Some parts can be quite frustrating.