Scaling factor forgotten after closing laptop
On a Dell XPS 13 9370 and an external Dell U2718Q monitor connected over the docking station Dell TB16, both being HiDPI, with gnome-shell 3.28.0-2 from Debian Sid/unstable in a X.Org session, I configured a scaling of 200 %. I have it configured as single display. Closing the laptop, and only using the external monitor, the scaling was changed to 100 %.