I was just getting started on a mix for a contest: organizing tracks, setting up buses, doing some basic track cleanup, etc. I had been saving my work regularly, but not as separate backup files. Then I either found a bug in my DAW or fat fingered something, but my project file got corrupted. Sigh....
So I decided to start over. There went an hour of work. I tried to reproduce the issue to no avail. All worked fine on the second go. Not the end of the world considering I was just getting started on the mix and it wasn't for a client.
Backups are free and easy. Don't forget to make them as you go (just in case)!