On wayland session logout greeter is broken on multiscreen (3 screens) configuration: it's displayed only on 2 screens (see attachment).
Created attachment 109400 [details] qdbus org.kde.KWin /KWin supportInformation
Created attachment 109401 [details] Screenshot
I remember to have done some fixes around the greeter. But those changes are only in master/5.12. I dare to mark as fixed. If you are still able to reproduce with 5.12 please reopen. Please note that 5.12 will show other bugs in the greeter due to bugs in Qt.