From an outsiders point of view... (assuming you didnt just buy this machine) If it truly is used for heavy scanning maybe consider a network scanner like the Documate 3920.
Is it possible there might be something on your firewall that is terminating the connection? Any tell-tell signs in your event logs? Try going into the port configuration and disabling SNMP comms. I had a situation where a printer would show online then randomly disappear and that was my fix.
Hope that helps.