It started happening after recent update (pacman -Syu) (~3 days back?).
My computer it set to lock screen after a few minutes of no keyb/mouse input. When i get back to computer and confirm my password, sometimes i have to wait 0-60 seconds with a black screen and only mouse cursor moving and changing its shape as i hover over various elements.
journalctl shows these recent messages.
dmesg shows these messages.
This issue seems similar: Black screen with cursor after login
but i do not have that folder that is suggested to be deleted and locate finds only:
$ locate “org.kde.plasma.eventcalendar”
Update: todays logins are instant, maybe it is about some overload, i do not know. But even this happened i have not noticed any slowdowns in interface before and after the delayed login.