As seen on screenshot, this error occurs after username/password input.
i modified /usr/share/sddm/scripts/XSession and changed
exec ck-launch-session $@
to
exec ck-launch-session dbus-run-session $@
and this resolves the issue above.
On a related matter, doing this also fixes issue stated here:
https://forum.obarun.org/viewtopic.php?id=1348
This test was done on a vanilla Xfce4 installation from obarun-install (uefi bootloader)