Hi, I've seen this problem on a fresh install of stretch on a Thinkpad T470s when docked.
I found another upstream bug: https://bugzilla.gnome.org/show_bug.cgi?id=709062 and a Fedora bug that was incorrectly closed: https://bugzilla.redhat.com/show_bug.cgi?id=876134 If I dock the laptop, press the wake-up button on the dock, open the lid and close it again the login screen migrates over to the external monitor. Regards, Daniel
