I started playing Halo reach on PC and realized achievements weren’t unlocking so I switched to xbox. Except now I cannot unlock the achievements for killing 7 moa in Winter contingency and reading the binary while aiming because I already did them on PC but the achievements didn’t unclock. I tried repeating them multiple times on xbox but the will not unlock.
I think some of the achievements might be bugged, as I also tried to unlock the kill 7 moa in Winter Contingency achievement as well but was unable to. I played on Xbox only, and have not tried MCC on PC at all just yet.
Achievements have been bugged since PC launch, just give them time to fix it. Your data should have saved for them so they should auto-unlock when they fix the issue.