I’ve seen numerous threads about achievement issues with this game, so I thought I’d throw mine in there.
I completed the Halo: Reach LASO playlist, on Xbox One X, solo, all missions in order, and didn’t get the achievement. It says 12/12, and nothing. I know there are issues with doing it in co-op and completing missions out of order, but I never played co-op, not even once.
I also know a possible workaround is to have someone give you a checkpoint at the Epilogue and finish Lone Wolf again. Anyone with a checkpoint to share that I could borrow to test this? My Gamertag is: bblcreator8790