I have a Dell XPS 13 9370 laptop with Ubuntu 18.04 and a Dell TB 16 Dock (Business Thunderbolt Dock). Since a few days ago, the laptop no longer works on the dock. When connected, it boots normally and I can log in. But about a minute after login, the laptop display and any externally connected monitor are turned off and the laptop seemingly goes to sleep. The power button light still indicates that it's on, and the keyboard backlight still goes on when I press a key (that's just a BIOS thing, I think), but the laptop otherwise doesn't react to keyboard input or mouse actions. The only thing that works is to press the power button for so long that the laptop powers off.
The same also happens immediately if I close the lid when the laptop is connected to the dock. (In the past, it would turn off the internal display and make the external monitor the primary screen, where the Gnome Shell Dash is shown, which is the desired behavior.)
A connection to the (powered) dock is enough to trigger this behavior -- it happens even if no devices are connected to the dock. Any suggestions what's wrong here and how to fix it?
