Did a few missions, come back later and all progress is gone. So I start over and get to the same point and then it deletes itself again.
If I stop playing campaign then it just keeps deleted itself. It’s unplayable unless I beat the whole thing in one sitting.
If you follow the whole thread for this problem (which I understand is reaaaaally long to read due all the people with this issue) You will see some players have the same issue, including myself.
The only good news we have it is that they will unlock everything you have got so far regardless the walkthrough you have done. In short, you will get back anything you got before.
This issue is currently being tracked here:
https://www.halowaypoint.com/en-us/forums/f0258e8001734968984e8b56990f8daf/topics/progress-unlocks-lost-deleted-issue/65dab4f5-d9e0-432c-af6a-dc062a3eec18/posts