If you’ve noticed that your knetworkmanager is no longer functioning, likely NetworkManager has gotten it self into a bad state. This can happen on unclean shutdown or crash of the NetworkManager application. That said the solution is quite simple

In a terminal session type:

sudo stop network-manager
sudo rm -f /var/lib/NetworkManager/NetworkManager.state
sudo start network-manager

This will remove the stale NetworkManager lock file and allow for proper operation. You should now find that knetworkmanager is functioning properly again.