On Sat July 14 2018 14:38:56 Stefan Krusche wrote:
> (Manually) changed /etc/X11/default-display-manager back to tdm-trinity

This broke your installation and invalidated subsequent tests as
/etc/X11/default-display-manager no longer matches the value
in /var/cache/debconf/config.dat

dpkg-reconfigure is the way to go.

--Mike