This happens on a virgin digitalocean droplet with only Ubuntu 18.04 & Virtualmin installed (clamd disabled and clamscan enabled).
I have run countless reboots & reinstalled afresh again and again & 30%+ reboots, result in a dbus error.
This situation is silent and undetectable unless you actually check if firewalld is running after reboot, or you will never realize it is dead!
This is quite serious in my opinion.
Are you also finding this to be an issue in your installations with Ubuntu? (run a dozen reboots and check your firewall)
Your input is of great significance. Eagerly awaiting your responce.
I opened a bug ticket here https://www.virtualmin.com/node/66358 with some additional attachments.
Jun 20 09:28:35 ns1 networkd-dispatcher: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.FileNotFound: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
Jun 20 09:28:35 ns1 systemd: networkd-dispatcher.service: Main process exited, code=exited, status=1/FAILURE
Jun 20 09:28:35 ns1 systemd: networkd-dispatcher.service: Failed with result 'exit-code'.
Jun 20 09:28:35 ns1 systemd: Failed to start Dispatcher daemon for systemd-networkd.
Jun 20 09:30:16 ns1 networkd-dispatcher: No valid path found for iwconfig
Jun 20 09:30:16 ns1 networkd-dispatcher: No valid path found for iw
Jun 20 09:30:16 ns1 networkd-dispatcher: WARNING: systemd-networkd is not running, output will be incomplete.
Jun 20 09:30:16 ns1 systemd: Started Dispatcher daemon for systemd-networkd.
Jun 20 09:30:16 ns1 systemd: Started firewalld - dynamic firewall daemon.