Ok this is kinda irritating I played through the first 5 levels of the campaign the other night with my one friend on Legendary, even have all the achievements and such for everything, including some of the level based achievements and such, and I go to boot up the game this evening to play some more and continue from where we left off and for some reason it says I have 0 progress on the campaign at all, no skulls/terminals or level progress to load from wtf 
Bump, a little help if anyone knows how to fix this or has had this problem?
It’s not fixable.
Samething happened to me. Sometimes it saves, sometimes it doesn’t. It’s best to do a level, then turn your console off, then back on to see if it saved. If it didn’t then you have to do the level again, if it did then you’re one lucky sob.
Oh damn… I got 5 levels in with a buddy back in January. Haven’t played since due to me not being online. But I might come back to it soon. Fingers crossed our progress has been saved. :S
Try deleting your profile and recover it on Xbox LIVE.