SoftEther VPN User Forum

you are sure, that your OpenVPN traffic was routed through the VPN-Server? Because 50 mbps looks high for OpenVPN on a VPS. But obviously, I don't know your VPS specs.

And please post something about your used Configs.

SecureNAT greatly reduces SoftEther throughput.

Using a local bridge helps a lot. (but is a bit harder to configure)