Intermittent packet loss

I've having periods of 3-5 seconds of total packet loss every 10-30 minutes.  The interruption does not last long enough to impact streaming video but is annoying for work-related video/voice communication and incredibly disruptive to gaming.

I've run simultaneous continual ping tests from my PC to the modem and to Google/Yahoo.   I have seen no loss to the modem - only loss is seen to the internet pointing to an issue with Xfinity's network.

The Xfinity app recommended a modem upgrade and today I received and installed an XB8 to replace my XB7.  The problem persists.

I've had this service for more than a decade and this problem only started to occur in the last couple of weeks.

How do I get this resolved?