tl;dr I’ve completed 5 missions on Legendary legitimately, but the game only acknowledges 3.
Now for the full story. When I first got the game, I beat all of Halo 2 with Scarab and Bandana skulls. After finding out they disabled achievements, I decided to do it on co-op. I teamed with this one dude and got The Arbiter and The Oracle achievements. Those counted toward Legend. Sweet.
Okay, here’s where things started to go downhill. The next day I do Pillar of Autumn co-op (which I had already completed solo on Heroic), but upon completion the Xbox boots me to the dashboard for some unknown reason. I start MCC back up. Co-op Legendary completion was counted, but progress on the Legend achievement wasn’t. This pissed me off. Am I going to have to do it again to have it count, just because the Xbox decided to quit the game on its own? This is bull.
The day after, I beat the mission Halo. It counts. 3/40. At this rate, I should have Legend in about a month.
Onto today. I got through Truth and Reconciliation, but somehow the difficulty was defaulted to Heroic. Sucks, but it’s Sunday and I have all day, so I’ll just beat it again on Legendary. I do so, then check my progress on Legend. It’s still at 3/40.
What the hell is going on here? Do they only count toward Legend if you unlock the mission achievement on Legendary? I hope someone has some answers.