When a Mission is active, most all MM screens ping the Internet every 30 seconds or so. Its always looking updated mission information. The more computers logged into a mission the more often a ping should be running through your network. The problem you describe sounds like something mucking up in the hardware - unfortunately.
An experiment you might try is to open something like stock quotes in a Google page. This would cause a ping every few seconds or so. If a shorter ping time helps with the issues, maybe we could look a MM feature that would help.
Mike