The problem is somewhere in the ISP's network based on traceroute information.  The traceroute dies before it even reaches the server.  It is possible that US West has enough IPs pointed at it that the long poll is causing enough packets to flood in/out in a very short timespan and its tripping the DDoS filtering.  Or it could simply be an unrelated hardware issue at the ISP that needs fixing.  Will know more once I get a response.

I know for the miners out there it sucks to see these dips of efficiency due to idles (luckily not too long), but the good news is that this time the problem is not in server hardware or software configuration.  If this is an accidental trigger of the DDoS filters,  it may be as simple as the ISP whitelisting our IP from the DDoS filters unless we ask for it to be turned on.