I've developed my own workaround as still waiting for my callback from Line2 support.
Stopped all deployments, rebooted all pc's, restarted Solus Deployment service on the server and manually installed the update on a few machines that were struggling with deployment throwing tcp errors.
The agents are now connecting and staying connected. I can also manually deploy via the Applications tab in Solus Agent and redeploy the agent from the server.
Gone from >100 systems missing the update for more than 3 days down to less than 10 that I'm having powered on to update. (No WOL, grrrr).