I just suddenly started having issues using VPN Manager for OpenVPN on mine as well. My issue just started yesterday. Booted libreelec, VPN manager tried to authenticate through Nord, but then it tells me "Could not authenticate with VPN provider. Please check user name and password and try again." I'm not sure where the issue is yet, because this happens on 11.0 and 12.0 nightlies. It was fine on both of those Friday/Saturday.
I know it isn't my username and password, because I as well am logged on through my laptop. I've changed 0 settings in the app in Kodi for both 11.0 and 12.0. I also tried to update the add-on, but there are no updates. I'm using the add-on from Zomboided which is 7.0.1.
It just randomly stopped working. I'll test it later today. Unfortunately I don't have another VPN provider to try with to see if it's a Nord issue or not.
So i have had the same issue, i have managed to get my NordVPN to connect. I don't know if this first part is relevant however in my process i have updated the VPNManager by zomboided to version 7.0.2.
Once the VPNManager tried to run a wizard to which i entered my user name and password, it failed with the same issue.
After exiting the wizard i entered the 'setting' of 'VPN Manager and noticed the token was blank. i logged into my Nord account via the url displayed and generated a access token, entered this then re-ran the wizard and the connection is succesful.
It would appear that Nord is enforcing the use of an access token. i cannot recall entering a token before, but i haven't had to change anything in months.