Frequent brief VPN interruptions

I've been having my VPN connection freeze for over a month. About every 5 minutes, I get a 10-30 second pause during which the mouse pointer moves but doesn't respond to clicks or context changes (changing from an arrow to a hand when you over over specific areas, for example). Response then resumes spontaneously. I'm also noticing an SSH connection to a different server now drops 1-3 times a day, and this is also new behavior.

What I've done so far:

Worked with my company tech support. No problems found and no other users have reported problems. There are hundreds of users in my city and most of them likely also use Comcast.

Checked with the SSH server administrator--no problems for them, either.

Tried a Windows machine instead of a Mac.

Ran a constant ping log. A few gaps were noted, but not often enough to correspond with the much more frequent problems I'm seeing.

Reset the router, probably seventeen times, with whatever firmware updates Comcast sent to it. 

Turned bridge mode off.
Turned bridge mode back on.

Used WIFI only.

Used Ethernet only.

Replaced the router three times, now on a rented brand new hot stuff XB8 whatever that the tech on the phone insisted he "knew" would fix my problem, though he couldn't say why. The purchased router I had did show some critical errors in the event log, but I don't know how to get to the event log of the rented modem.

Had three visits from techs inside the house and had outside wiring checked as well. Had "a ticket" opened on the "the server side" with Comcast and I've been told everything is fine. 

The last tech I got online opened a ticket with the "advance" team, but I don't know what that means.

Anybody have any other ideas that don't involve me using DSL for VPN and Comcast for everything else? I don't much like that idea.

I'm happy to install and run appropriate logging software if needed.