Recently NordVPN upgraded their client program. Unfortunately the new version does not work on GalliumOS. Once it tries to connect to the network, it fails saying you need to contact customer support. In the process it nukes your network connection, and seems to need a reboot to recover from.
In the past I have used a manual connection, using the 'Network Manager'. One of the reasons I moved to using the client was that this was unreliable. Many of the servers I would try to connect to wouldn't work. If one did work it typically did so for a while. When I attempted to go back to using this mechanism it didn't work.
On contacting NordVPN support they said that I needed OpenVPN version of 2.4 or later, whereas Gallium OS is on 2.3. So hmmm, how to upgrade?
GalliumOS is based on Xubuntu. Typing...
reveals it's actually based on Ubuntu 16.04.
I eventually found the following. I had to make a few small tweaks to make it work for me...
sudo curl -s https://swupdate.openvpn.net/repos/repo-public.gpg repo-public.gpg sudo apt-key add repo-public.gpg echo "deb http://build.openvpn.net/debian/openvpn/stable xenial main" > openvpn-aptrepo.list sudo cp openvpn-aptrepo.list /etc/apt/sources.list.d/openvpn-aptrepo.list sudo apt update sudo apt install -y openvpn
The changes were only to split commands to avoid permission issues. Hopefully this helps someone out there.
In terms of trouble shooting OpenVPN connections you can just use the command line with one of the openvpn config files downloaded from NordVPN. For example
sudo openvpn someserver.ovpn
It will ask for username and password, and these are the username and password listed in your account page in NordVPN. It's not your username and password to login to NordVPN.
The information dumped to the terminal gives details about connection issues. Interestingly before I upgraded, if I connected to a NordVPN server via the command line it worked, but if I connected via network manager it didn't.