Hey guys LoneStar here.
Is anyone else missing achievements that they previously unlocked? I have huge chunks missing including many for Reach and all of my Halo 3 achievements. If fact it shows I have never played Halo 3. I wouldn’t consider myself an achievement hunter but some of those where really hard to unlock and its a shame they’re gone.
Either you got a Gamerscore reset or you earned some of the achievements offline and did not synch your profile before you downloaded it.
If you have changed your gamertag since playing those games then your Waypoint profile will be out of sync. You would need to play them again on your new tag in order to get things syncing again - this can be anything from campaign to forge, as long as you’re connected to Xbox Live when doing it