I have the same problem on a 2017 XPS 13 running Windows 10. When I unplug from the Dell D6000 docking station it's a crapshoot whether or not the apps I had running on the external monitors will scale correctly when they get moved to the internal screen. I also run into problems if I plug into the docking station after booting, it frequently doesn't recognize the external monitors (also Dell branded). In order to get everything to work correctly every time I need to shutdown before connecting to or disconnecting from the docking station, and also make sure the monitors are turned on before booting while connected to the docking station.