I have a problem with login screen.
1) After boot-up the login screen appears with correct resolution (i.e. my default 3200x1800). However, after a fraction of second it changes to some ~1600x1200. After login everything is back to normal.
I know that this is "standard" problem with two displays. And that this should be solved (but it didn't work for me) by some (e.g., here)
xrandr script added to lightdm. However, I have just single screen (rarely I attach some external screen to give presentation).