Big huge bug, not sure how this got by. My son logged into his account on the same Xbox earlier, then I logged back into mine. And my campaign save was gone. All saves wiped. So I tried an experiment. I created a new game, skipped the cutscenes, got to the part where you move the head in the first scene. The little text pop up actually says “save failed” on the left side. I exit the game and verify that I can see something to load. Sign out and into the other account. Sign right back out and go back into my account and start halo again. No saves. Wiped again.
Anyone else experience this? Try at your own risk of course.