I think something similar happened to me too, in the middle of a thight deadline (I know, silly me to update but I really wanted to take advantage of proxies and scatter).
The file went corrupt (incorrect file structure) and upon opening it for recover (win: create C4D shortcut - shortcut Properties - modify Shortcut Target adding a space and then -loadcorruptscenes),all the Cameras where missing (?).
Unfortunately the recovered scene was unusable but I managed to open the corrupt file and save it in R24 where I had not updated Corona, from there I had to redo all of the scatters and the cameras back in R25.
Thing is, I had another corrupt file "incorrect file structure" on the same project after a while and I really think that in this case the Camera Tag was added in Corona 8. Anyway, I'm working in panic mode since :( .