So I recently had finished Halo 3 legendary campaign. I’d run both Halo CE and 2 prior to this as I was, and still am, going for the Legendary achievement. However according to Halo Waypoint I’ve not completed Halo 2 or CE, but my game shows it was completed in legendary difficulty. I’m honestly upset at this and was hoping there would be anyone who could help instead of me running that whole fiasco again.
Did you complete all the campaigns while connected to Xbox Live? According to your service record, you completed only Halo 3 campaign.
Also, you can leave feedback in the Achievement Progress Thread.