Before the problems with your servers, everything was fine, even with the "intermediate node" the speed between my server and the client was stable, I'm not talking about direct tunneling.
After your servers crashed, the problems started horrible.
You write that the work of RadminVPN in Relay mode is regular - I understand, but why before the failures of your servers, problems with ping and speed were not noticed, but now everything seems to be implemented with DSL Internet at a speed of 1MB. Which way to look? problems with ports and firewall (both on the router and in the system) are resolved, there is a white SP. There are other services hanging on it and the ringing goes quietly before them .. Will you tell us, dear, what should we do? I repeat, all the problems started after your servers crashed.
We are working to increase a performance and connection speed. You can also check if there is no programs that overload your network, like FTP, torrents of Windows updates.
And the more Radmin VPN networks you are in, the less performance you have.