Is everything gone?

I worked on a project for a while using DaVinci Resolve 15. I worked on this project earlier today for a few hours and hit 'save' several times and also saved the program before closing it. Some hours later, I relaunched the program and found the day's saved work, not saved. I also got a message, that the program can no longer save the project. I did a save as, and it saved as a copy. But I still lost the day's work. So then I figured, maybe an upgrade from 15 to 16 would fix the save issue. I upgraded and discovered that not only did I lose the project I was working on, but all projects I worked on. Is there a way to retrieve it or is everything pretty much gone now? Surely the working files are still on my machine somwhere...? And yes, I have more than enough space on my machine. So it is definitely not a space issue. Adendum: I looked under 'program data/Blackmagic Design/DaVinci Resolve/ Support/Resolve DiskDatabase/ResolveProjects/Users/Guest/Projects====> and there the Project.db file is, but Resolve cannot import it. Any ideas? Further adendum: Okay, so I downgraded to 15 and got my files back. So I want to continue to work on my project but know that hitting 'save' may or may not work. So how do I make sure my work is saved after a session, because 'save' is becoming a coin toss.

I would talk to BMD Customer Support about this (phone numbers elsewhere on BlackmagicDesign.com), but I always export a .DRP copy of the session on an external drive just to make absolutely sure I'm backed up. I almost never have had to use the backup, but it's nice to know it's there.

Why does 'save' stop working? It's not a back up issue. Nothing crashed. Everything seems to be working fine until I launch my project and see my day's work missing. Adendum: I went back and redid the work of the previous day and it seems to be saving, only now the program crashes when I group select and move footage, 100% of the time. Fun times. This is DaVinci Resolve 15.3.

Be sure to read this:

viewtopic.php?f=21&t=90190

Make sure that your drive containing the database (probably c:) is not full. Just on the off chance that's the problem, and only takes a few seconds to do.