I finished the campaign for Halo 3 last night and didn’t get the achievement. I came here and checked my service record, it said I hadn’t completed the level Cortana. I went back and completed the level again, but it didn’t update. I power cycled my console, tried again, and no luck. I tried once again today and it still just won’t show up as completed. I’ve also gotten under the par time 2/3 runs and haven’t gotten that achievement.
I’ve been playing through without any skulls on normal difficulty. I haven’t been saving and quitting in the middle of the level or doing anything out of the ordinary - just starting from Halo 3 mission select at rally point alpha. Can anyone advise me on a way to make the level register as complete?
Edit: Tried again after making this post and it worked. No idea why. I didn’t do anything differently. These achievements are just buggy.