If I restart plasmashell, or my computer, favorites and history in the app launcher (kickoff or alternatives) are gone.
I'm on Arch with the last updates.
I have the same on my laptop with master branch.
I got this bug too on my PC running manjaro with the latest updates.
Confirming this one. Logging out, restarting, switching users will clear all history from all the launchers.
*** This bug has been marked as a duplicate of bug 385814 ***