After updating (openSUSE 20180129, I think) a few days ago, one of my four computers on openSUSE lost all of the favorites from the Kickoff application launcher. I’ve tried - with no luck - to determine where they might be stored.
I’ve done numerous ‘Add to Favorites’ reloads, but it’s always kaput after logout/login or reboot.
They are stored in kactivitymanagerd since a while, to allow different Favorites per activity.
Maybe try to remove its database, ~/.local/share/kactivitymanagerd/, it might have become broken for some reason.
You’ll also lose the recently used applications and documents though.
Btw, there haven’t been any related updates in the last few days.