Running Zimbra Network M4, every couple of hours most of the Tomcat system goes down. IMAP dies (still listening on the socket but times out on connect), and users cannot log into the web interface (can log in, then sits at "Loading ..." screen indefinitely. None of the Zimbra or Tomcat logs contain anything that could be perceived as indicating any sort of problem. When trying to restart Tomcat, a "java.net.ConnectException: connection refused" error is encountered; the process needs to be killed manually, and then restarted. It's driving our testers nuts.

Anyone have any ideas what's up?