Sorry, just got home.
Thank you very much !

Thank you !!!
I can confirm that removing virtualbox-guest-common "solves" the issue.

This time the jingle played in tty before I killed VBoxClient. But only after killing VBoxClient and connecting second screen I get the Desktop back.

Do I have to kill anything first?
If I go to tty after boot and run /usr/bin/budgie-desktop (as root?), I get no messages at all. Once it said "terminated" though.
But I noticed the following: I boot. I enter username ans password. For 1 second it displays my normal Budgie Desktop, then the screen turns black. Then I go to tty and kill the process VBoxClient. Then I hear the jingle Budgie plays at startup. Then I switch back to Ctrl+F7. If I now connect a second screen, I get my Desktop back.

No: AMD® Rv620

I updated via terminal with sudo eopkg up

Please take also in consideration todays developments in: #179

Well, please keep in mind that I am not a programmer and don't really understand these things.
Since simple-scan itself got also updated this weekend, I did some testing.

I am using a Canon CanoScan Lide 100.
But I am not sure if this is a sane-backends issue, since :