Avast-prompted reboot trashed my computer.

last night (around 12:30 am, 5-10-2017) Avast popped up a message after I switched between my 2 user accounts on windows. The message said that Avast needed to reboot the computer to apply updates. This appeared routine, so I clicked on reboot. After the reboot, the computer was seriously messed up:
-screen resolution set to 800x600 (I always run 2560x1600)
-right-clicking desktop\screen resolution only brings up a limited selection , maxing out at 1280 x 800.
-desktop settings reset to windows default. (wallpaper, windows theme, etc)
-my desktop icons were missing. only a few program & windows icons remained.
-My documents folder was now empty! (freaking out now)

I immediately performed a system restore to 2 days earlier.
after reboot, the screen resolution is now restored but my desktop settings are still missing and my documents folder is still empty.
A second reboot lets me see some windows messages that appear briefly:

  • just before the desktop appears , windows says: “preparing your desktop” I don’t normally see this.
  • after desktop appears, a windows popup appears in notification area saying (something to the effect of) that this is a temporary desktop and to try and log in later.
    hovering over the Avast icon in the notification area caused it to disappear.

A third reboot was no different, but after a few minutes, the Avast UI popped up (of its own accord) with the familiar “You are now protected” message.
A forth reboot restored my desktop setting, icons and My Documents files.

It appears that I’ve managed to restore the computer to a working state but I’m still very concerned as to what caused all of this.
After checking this forum. I find the last Avast program update was 7 days ago… why is Avast asking to reboot a week later?

Thanks for any help & apologies if the post is too long (my 1st post)

that this is a temporary desktop
That sounds like a bug that is already fixed.
After checking this forum. I find the last Avast program update was 7 days ago
No, it was not. Last update was (iirc) 2 days ago. You will not see it in the history list or by looking at the version number as they where micro-update/micro-fixes.

Not saying it is, but the problems can have to do with the updates MS rolled out recently.
Perhaps the combination of both the MS updates and the avast updates has caused the problems.

Unless you have something like logs that have (at least) a indication, it is mostly hard to tell if not impossible what was causing the problems.
There are really a lot of possible causes.
Even a real tiny hiccup (even if it was less the then a millisecond) in the power can have caused it.