$ kmix QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave. QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave. KGlobal::locale(): Warning your global KLocale is being recreated with a valid main component instead of a fake component, this usually means you tried to call i18n related functions before your main component was created. You should not do that since it most likely will not work unnamed app(16431): Communication problem with "kmix" , it probably crashed. Error message was: "org.freedesktop.DBus.Error.NoReply" : " "Message recipient disconnected from message bus without replying" " Reproducible: Always
Klocale implies KDE 4. Please confirm if still a problem with current KMix and Plasma 5.
I would expect it has been fixed at some point since 2016.