pfSense

If the OpenVPN server interface is selected in the ntopng 'General Options' - 'Interfaces', it causes thousands of OpenVPN server error logs at random intervals.

The OpenVPN server logs say - 'error - IP packet with unknown IP version=15 seen'.

No clients need to connect to the server to cause the errors to start at random.
It is not a problem with server-client compression, even though that can cause same error messages (as mentioned, no client needs to connect for errors to start).
Clean reinstall does not solve the problem.

After deselecting the OpenVPN interfaces in ntopng 'General Options' - 'Interfaces', no errors occur.

I can reproduce the problem by selecting the OpenVPN server interfaces in ntopng settings.

More details and troubleshooting can be found at the forum thread I opened in 2021
https://forum.netgate.com/topic/166112/error-ip-packet-with-unknown-ip-version-15-seen

The problem was fixed couple of days ago
https://forum.netgate.com/topic/166112/error-ip-packet-with-unknown-ip-version-15-seen/10?_=1680269984466