Run tcpview and check what is the remote endpoint, it will provide you knowledge of what cause it.
Edit: I seen your result from tcpview. Please know that multihoming a DC bring challenge.. As such your tcpview show that it’s your own server that talk to itself. A badly binded ADDS service to your WAN IP is the culprit. Be advised the traffic never ...
Here are the steps which resolved the issue mentioned by Martin.
Backup C:\Program Files\OpenVPN\config
Uninstall tap adapter and openvpn from add/remove programs
Download and install latest OpenVpn package (openvpn-install-2.4.7-I607-Win7.exe)
Copy the backup config to C:\Program Files\OpenVPN\config
Start the OpenVpnService service and ...