logs
I can't see anything specific, but reading logs and interpreting them is not my forte. Maybe someone sees something there.
/etc/openvpn/nordvpn_france.ovpn
You added at least 2 entries: up /etc/openvpn/updns and down /etc/openvpn/downdns. These are not supplied by NordVPN as far as I know. I don't think this is needed.
/etc/config/dhcp
Your config dhcp 'lan' file contains NordVPN DNS servers and Google DNS servers. This isn't the right place for them. Also you should be fine with just the 2 NordVPN DNS servers.
Have a look at this: 5 steps guide to set up an OpenVPN client with NordVPN in Luci.
This is the easiest way I found to set NordVPN on my router as a client. It is basically the Luci version of the official guide from NordVPN to set a client in OpenWRT (minus the kill switch part).
In case you struggle with creating the network interface, have a look here.