Whenever Manjaro KDE starts, Yakuake is summoned from the menu bar and must be manually dismissed with F12. The solution is to disable Yakuake on startup:
System Settings >> Startup and Shutdown >> Autostart >> Uncheck to disable Yakuake . Yakuake can still be summoned with F12 but just won't show as unfurled on startup.
I'd recommend setting this by default so that other users don't have to do this manually. (If the goal is to show users that the feature exists, there are better ways to do so besides having to close the drawer on every startup in perpetuity.)