Achievement help!

Man I beat the Halo Reach LASO playlist but the achievement won’t pop. Please help I can’t go through that again. Help!

I checked your service record, and I assume you did it in co-op. Noble Actual does not result completed on legendary. The rest of the missions are though.

I have seen this before, people had this issue where cutscene missions won’t register for them (The Heretic from H2 is also an example), they do only for the host. As a consenquence, the achievement pops for them but not you. Sadly to get around this, you’d have to play these cutscene missions solo first, and then once you land in Winter Contingency (or in Cairo Station for H2), you bring in your friend and go on. I am afraid you’ll have to redo it again.

Halo Completionist explains this in this video at 0:21, if you want to take a look.