Not really a bug but a suggestion for an enhancement. 

Krunner on first usage takes significantly longer to start up upon the activation being used as it takes time to start the krunner program. This feature is meant to be a convenient "Quick search", and having to wait a few seconds for it to run (Even longer on slower devices) takes away most of that quick searchness. The MacOS spotlight search appears instantly. It also leads to missed keypresses if something is typed while waiting for it to launch and all of this led me to not wanting to use the feature even though I love it!!

My suggestion is very simple, make krunner daemon launch in the background on device startup. This is already possible through setting up a startup service for krunner, but I think that it would be helpful for this to be in default KDE because it would just make the KDE experience so much more seamless, smooth and quick.