I think I have messed my system: I can’t log out or switch user from the logout panel.
I am using Ubuntu Mate 18.04, Mutiny layout.
When I try to logout, the panels just reset and reload, with some strange duplication of widgets. It also disables the touchpad, making the computer more difficult to use.
Trying to switch user does nothing except becoming unresponsive for some time.
I think this is related to LightDM, but I can’t be sure.