Windows 10 PC "travels back in time" ??

I left the PC on overnight and when I checked it next morning, there was picture on the monitor. I was in a hurry and hard-rebooted it. Then I noticed something really strange! The last couple of days of activities were missing!

• When I opened Vivaldi browser, it was re-loading the tabs I browsed a coupled of days earlier. Not the tabs from the night before.
• When I opened Qbittorrent, all the torrents that had been downloading from the night before, were missing, and only those that had been seeding a few days back, were visible.
• I had also updated the beta version of a software called Scrivener the night before -- but when I opened it, it was still at the old, expired Beta version that I had upgraded from.
• I checked History in the browser, but there was no history from the day before, even though I spent ages on the net.

It was like the computer had forgotten about the last few days and just rolled back. But this is a brand new machine, it has no backup at all set up.

• Is this a known phenomenon?
• What on earth happened?
• Any way to restore the user profile (that seems to be what took the main hit).

I'm very technical, working in IT etc - so don't hold back and don't dumb it down if you've got any serious feedback on this. I am just very surprised by this and I can't figure out why a hard reboot should cause the computer to lose so much. I believe that data in the AppData User folder is primarily what's missing - but how could this have happened? I'd like to understand it just as much as I'd like to restore the lost work.

Uninstall vivaldi. many people have complained about it. Its not a good compared to others btw