"Pulling the network down" is anything that keeps the network from communicating. An open or short or a module that has something causing it to lose connection to the network. This would be intermittent due to cold solder joint, ground, loose wire or connection at a splice or block. You discovered what is pulling your network down when you seen the cluster working and you had communication with the network then the cluster not working and no communication. It's hitting you in the head so hard you can;t see it.