Ubuntu 18.04 does not switch between users after upgrade

This behavior could be related to gnome-session <-> desktop environment <-> windowmanager

1. Test the new account (C) with open new tty by ctrl+alt+F3, login with the given credentials and startx

2. Check your error logs with journalctl -p err -b and maybe post at pastebin.

3. Check if something is missing by i.e. dpkg -l | grep '^ii' | grep gnome-s.

3. Check your current environment by (see here)

   • Window manager: wmctrl -m
   • Session: echo $DESKTOP_SESSION
   • Desktop environment: echo $XDG_CURRENT_DESKTOP

   For me it is i.e. GNOME-Shell ubuntu-xorg ubuntu-GNOME, installed after dist-upgrade by install or reinstall

   sudo apt install gnome-session gnome-shell ubuntu-desktop-minimal

4. Solve the ecryptfs issues, see this answer

5. Option to remove compiz, see here (should work in the same way in 18.04)

6. After this steps it's maybe helpful to do a sudo apt full-upgrade