Update Jan. 2
The network system tray icon keeps turning itself upside down and back up again.....
I was unfortunately able to reproduce the empty task bar again by not logging in immediately after a reboot, but leaving the login/lock screen as is. When I did log in after a while, I got the empty task bar again. It was on the correct right side of the screen, but no task bar- or system tray icons.

And just like last time, right-click or ctrl-alt-del triggered no response/no action.
The Start 11 start button and menu did function -like last time- so I could reboot and log in, and all was well again.
The strange thing is that this does not happen when I sign out, and log back in later. Seems to only happen after a reboot.