common problem this seems to be happening to alot of people i was 62% thou the game and was only a few riddles away from finding riddler so annoying and it seems to be random cos i always switch off from the menu screen
Probably did like I did and shut it off whie it was saving. Didnt see the litte saving symbol and instead of cutting it off through the menu I shut it off with the xbox button. Atleast thats what I think it was. Weird thing is that I was at the same spot
you were at when yours vanished.