Thinking maybe if there's some problem with the wallpaper, we enter an error case from hell and open the doors, but I couldn't reproduce that problem when I played around with bad wallpapers.
Your extrausers file indicates that your user *does* have a password set. So it is unity8 that's the odd one out, not system-settings.
I'm still confused why this would happen. One other bit of useful logs would be /var/log/auth.log if you can upload that...
So in your unity8.log, I noticed the following interesting message:
file:// /usr/share/ unity8/ Greeter/ GreeterContent. qml:69: 5: QML QQuickImage: Cannot open: file:// /usr/share/ backgrounds/ Kronach_ leuchtet_ 2014_by_ Brian_Fox. jpg
Thinking maybe if there's some problem with the wallpaper, we enter an error case from hell and open the doors, but I couldn't reproduce that problem when I played around with bad wallpapers.
Your extrausers file indicates that your user *does* have a password set. So it is unity8 that's the odd one out, not system-settings.
I'm still confused why this would happen. One other bit of useful logs would be /var/log/auth.log if you can upload that...