Ok
I have just completed the weekly challenge off firefight and I had to turn my Xbox off because it was 2 am!! HA staying up late Playing HALO FTW!!!
The next morning It had said Welcome to Noble team as it usually does with new players, but I am not a new player. it has reset my armor and my campaign progress. it has happened to me 4 times already and i am getting sick of it!!!
Does anyone know how to fix it??? 
Delete your profile from Xbox LIVE and redownload it, as for the Campaign progress, you need to replay the Campaign.
Your armour should still be unlocked.
thanks. I just tried that and it reset again!!!
Are you sure you’re signed in to the right profile?
Have you tried installing/reinstalling the game?
It’s happened to me three times. I no longer care to play Campaign any more because of it. I get squat for credits for completing missions on Legendary so why should I bother replaying it if it’s just going to get reset eventually.
This is one of the things Bungie should have fixed before abandoning Reach, or 343 should have fixed a long time ago in an update. At least you get to unlock all the armor you’ve purchased for free.
Since we’re on topic: Hey 343 mods, your company has the ability to change pretty much anything in the game right? Why hasn’t this been fixed yet?
Thanks for your replies. I have tried everything you guys have said. But it got reset again today.!!!:-(:-(:-(