If I am correct, Autosave is saving on another file each X minutes, while auto-backup is copying the last file you saved before erasing it.
If you have a Test.Capx, make a change then save it once again, the Test.capx.backup should contain what the test.capx contained before the save, so if the save failed (or you made a breaking change that you cannot find out), at least you can use the backup file.
I hope I was clear
And that is why you shall respect the bug reports guidelines, not only giving a capx is making the bug reproductible in one click in a situation they can work with (less time wasted trying to reproduce vague instructions) but also it helps filtering false positives.
Game design is all about decomposing the core of your game so it becomes simple instructions.