i tried to track the issue a bit more, it seems the DISPLAY variable isnt
cleaned up fast enough in the environment after logout.
i can see in the ldm.log that the ssh connection was established correctly on
the second login attempt (see attached ldm.log), but was closed from the server.
as the attached xsession-errors file from the server shows, x-session-manager
exits with "cannot open display:". to make sure its not caused by any leftovers
from the former session i ran slay for the user between the two login attempts.