Achievement not unlocking - "Alone for One"

I’ve completed all the Halo 5 campaign missions on Heroic co-op according to my in game service record. However, my achievement tracker is stuck at 93% and hasn’t unlocked the “Alone for One” achievement.

Due to the achievement tracker’s progress, it seems that one mission hasn’t registered towards this. Which one that could be, I have no idea… has anyone had a similar issue?

Did the achievement pop for you?

Having the same issue stuck at 86%

Nope, it still hasn’t popped for me. The achievement tracker is still at 93%, but oddly enough my xbox.com tracker says 300% for this achievement.

I’ll likely just have to play through it again.

I recommend playing through co-op on legendary this time, it might supersede the info to make it work.

Same for me. Completed on legendary solo and my heroic and legendary achievements aren’t popping. It’s been a week and no dice. No idea what to do now