I have had the same issue too, I mostly play in sandbox mode. Its very upsetting and annoying for the game to do this, but I appreciate that its only just come out. Its very annoying as I said, that I was happily playing the game. Saving the game and coming back the next day to carry on but for some reseaon it doesn't save. I find that very odd for it to save one minute then for it to reset back to the second to last save you made. I do hope they fix this in a few days or a week. I'm just bored now as I know if I play it and turn off my Xbox and come back, my save won't be there please fix squad/flying tiger!