Hello,
Are you using Mobile SIM connection? Could you trysetting an MTU on the mobile interface in Network -> Interfaces -> edit Mob1s1a1 -> Advanced settings? I would suggest trying the following values to see if ones of them works: 1400, 1440 and 1500.
If that does not help, I would like you to replicate the issue and then generate a troubleshoot file. For this, upload the configuration file from NORDVPN and give your router a few minutes to try and establish a tunnel. Then, navigate to System -> Administration -> Troubleshoot and download troubleshoot file from there. You can attach the file by editing your question. The attached files are only visible to Teltonika moderators.
Kind Regards,
Andzej
