Halo 2 legendary achievement completion bugged

My friend and I recently completed the halo 2 campaign coop on legendary, yet for some reason it was not completed for me. I have every mission on legendary except the last three missions we just did today. All the other missions we did the past days on and off are marked as legendary completion. Do I have to redo the last three missions again because something is wrong on your end?

> 2533274859977231;1:
> My friend and I recently completed the halo 2 campaign coop on legendary, yet for some reason it was not completed for me. I have every mission on legendary except the last three missions we just did today. All the other missions we did the past days on and off are marked as legendary completion. Do I have to redo the last three missions again because something is wrong on your end?

According to your Service Record here on Halo Waypoint, the level “Quarantine Zone” was not recorded as being completed. Replay that mission again and the achievement should be unlocked.

the exact same thing happened to me. i played legendary coop with my friend as host and I have only the final three missions not marked as complete.