Getting "SshConnectionException: Client not connected" on RunCommand despite being inside "if (client.IsConnected)"

Here is my code:

private void connectToMacSSH()
{
    using (var client = new SshClient(sshIp,
                                        22,
                                        sshUsername,
                                        new PrivateKeyFile(rsaKeyFilePath,
                                        sshRsaPrivateKeyPassphrase)))
        {

            client.Connect();

            if (client.IsConnected)
            {
                new Thread(() =>
                {
                    client.RunCommand("caffeinate -u -t 2");
                }).Start();
            }
            else
            {
                ...
            }
        }
    }
}

This is how it's called (in a main method):

sshThread = new Thread(() => { connectToMacSSH(); });
sshThread.Start();

This code was working 100% fine just minutes ago. I have no idea what I changed, but for some reason, even though client.IsConnected returns true, running the client.RunCommand line will throw "SshConnectionException: Client not connected", every time.

The command itself executes fine on another SSH client, using all of the credentials and login details on another SSH client works fine too. I have physical access to the host I am trying to SSH into, it is on (logged in and screen on), connected on the right static local IP, and I can access it via other SSH clients.

I've rewritten the code about 3 times now with no success - I even tried removing the try catch block (around RunCommand) and the command itself from a new thread and running it synchronously instead - it had no effect.

All help widely appreciated, completely unsure of what to try next...

Someone else had this issue... only answer was a dead link https://stackoverflow.com/questions/25522894/client-not-connected-exception-with-ssh-net

Iniziare dal punto di ingresso connectToMacSSH fornito e dalla chiamata RunCommand, quindi esaminare il ciclo di vita della connessione del client SSH intorno alle varianti con thread e sincrona. Riprodurre l'eccezione segnalata usando le credenziali e il comando forniti e determinare se il comportamento è dovuto a un difetto della libreria o a una condizione del ciclo di vita specifica del problema prima di definire un test di regressione o un aggiornamento della documentazione.