ssh.net forwardedPort stops after 'x' minutes

[digital-telemetry]

I'm using ssh.net, with a forwardedPort. After 'x' minutes, the local forwardedPort listener goes away.
I am using keep-alive settings for the main openssh connection... that connection stays alive. But the forwardedPorts() collection is dead.

Any ideas? How to keep them alive?

I tried forwardPort.stop/start to resurrect. Doesn't work.
I tried querying the ssh.net client object for hints... all objects still "not nothing" and looking good.
But netstat proves the forwardedPort listener is gone.

My current solution is to pre-empt every connection attempt with the .NET equivalent of netstat... and drop/create the entire connection if required. Seems a bit heavy handed.