If I do "sudo systemctl restart NetworkManager.service" networking works just fine after the restart, but the network icon/widget disappears from the system tray. Reproducible: Always Nothing about NetworkManager or "nm" appears in $HOME/.xsession-errors
Plasma-nm is loaded based on whether NetworkManager is running by checking its D-Bus service. I guess there is some problem with re-checking the availability on plasma side. Is the problem reproducible everytime?
Trying to reproduce it some, it seems to actually be intermittent. Also, on one of the network restarts the NM systray icon was still present though it wasn't working, and didn't disappear until I tried clicking on it.
Looking in /var/log/messages, I see these lines which might be relevant: Aug 20 00:51:42 localhost kdeinit5: kf5.kded: No X-KDE-DBus-ServiceName found in "/usr/lib64/qt5/plugins/kf5/kded/networkmanagement.so" Aug 20 00:51:46 localhost kdeinit5: networkmanager-qt: void NetworkManager::NetworkManagerPrivate::propertiesChanged(const QVariantMap&) Unhandled property "AllDevices" Aug 20 00:51:46 localhost kdeinit5: networkmanager-qt: void NetworkManager::NetworkManagerPrivate::propertiesChanged(const QVariantMap&) Unhandled property "Devices" Aug 20 00:51:46 localhost kdeinit5: networkmanager-qt: void NetworkManager::NetworkManagerPrivate::propertiesChanged(const QVariantMap&) Unhandled property "GlobalDnsConfiguration"
I'm not sure whether this is actually a bug in plasma-nm, because it's plasmashell who loads/unloads applets based on DBus services.
Fixed in 62ac5cd17b00a5e85eb629c4cce44b6f57d6a7fc will put in 5.7.5