Catalina 10.15.2 update wiped all files on iMac

I upgraded from Mojave to Catalina 10.15 in October. Since then I had been getting regular updates (automatic) and hadn't had any problems. Two days ago, on a restart, it looked like it was updating. Took about 20 minutes. Upon booting up, I got the "setting up your Mac" screens. When that was done I noticed everything on my desktop (and any other file I had had) was gone. Preferences were gone also; e.g., dock in default position, mouse not set up, MS Office asking me to sign in etc.

I looked in the "relocated items" folders. Nothing there, and I can tell from looking at the storage tab that everything is gone. I hadn't had anything going to iCloud but I checked anyway. Nothing there. The files were backed up and it was not my main machine so it isn't a heart-breaker, more just annoying and now time consuming.

So, I figured, "Oh well" and started setting everything up again, files, preferences etc. Lo and behold, after a few restarts, the same thing happened again! Got the "setting up your Mac" screens again and everything had been wiped again along with the preferences I had been setting up.

By the way... I had tried a fix I read about where I created a new user to login as, logged out, restarted, etc. That didn't seem to have any effect.

What do I need to do? Completely reinstall Catalina?

Configuration:

iMac (Retina 5k, 27 inch, Late 2015)

Processor 4GHz Quad-Core Intel Core i7

Memory 24 GB 1867 MHz DDR3

Graphics AMD RadeonR9 M395 2 GB

Catalina 10.15.2