Oh, Ive found something in journalctl :)
plasmashell[3223]: kdeconnect.interfaces: dbus interface not valid
QDBusError("org.freedesktop.DBus.Error.UnknownInterface", "No such
interface 'org.kde.kdeconnect.device.notifications' at object path
'/modules/kdeconnect/devices/a3ca5b1>
It doesn't make it clearer for me though. If nobody else sees this I'm headed for
bugzilla.