Latency spikes every 12 minutes exactly

Hello,

I'm experiencing brief but high latency spikes exactly 12 minutes apart, all day every day, on every device on the network.  I'm not sure how long this has been going on, as it's only noticeable while gaming (I assume streaming services operate with enough buffer that this type of spike does not disrupt viewing), however I've been observing it anecdotally for at least a month. I know it's a relatively new problem, since I've lived here for two years with no changes to the network configuration (no new devices, same router they shipped me when I moved), and never noticed any problems until recently (and I do game with some regularity).  I can't pinpoint exactly when it started- maybe sometime in May or early June?  Maybe earlier and I wrote it off as regular incidental lag spikes.

I use the rented modem/router combo with no additional network gear (no bridges, no switches, no wifi repeaters, no extra router).  My primary PC uses a wired connection directly to the router (nothing going through the walls) but I've also observed the same latency spike on devices connected via the wifi (including on my primary PC, which I briefly switched to WiFi for diagnostic purposes).  The latency spikes do NOT occur between local addresses (tested PC to laptop, both directly connected via ethernet to the router).

Here's a 6 hour sample from PingPlotter from a few days ago (but accurately represents what I've observed every time I've checked):

I realize that might be hard to look at (not sure how it will be formatted in the actual post) so here's a smaller, more granular view of the actual instances:

It might also be technically significant (we're getting outside my knowledge now but I want to provide as much detail as possible based on my observations) that each spike appears to consist of two separate, observable spikes (this corroborates my anecdotal observations while gaming, which is two lag spikes back to back):

                   

One spike is sometimes much worse than the other, but as you can see in the examples above, it does vary.  Some of the spikes I recorded even appeared to be a single spike, but I was using a 2.5 second interval on pingplotter, and because of the regular intervals, I think they were just reported as a single spike as a result.  One such example:

If it would be diagnostically useful, I'd be happy to run another trace using a more granular interval (ping plotter goes as low as .5 seconds, at least it does until my free trial runs out lol).

I have already attempted:

-different device (latency spikes observed on two PCs and one laptop on the network)

-different cable

-test LAN latency (none observed)

-reset router locally (unplug, wait 30 sec, plug back in)

-reset router remotely (using Xfinity app)

-test connections remotely using Xfinity assistant (reported everything looked fine)

I've seen several similar issues posted here on these forums (all reporting between 10-12 minutes between latency spikes), both recently and years ago.  Most resulted in the user being asked to DM Xfinity support, which I would love to do but I see no messaging interface here, just the "bell" notification tab and the user profile. 

I also haven't been able to even find a number to call for tech support.  Believe me, I am the last person who wants to get on the phone with anyone, especially customer support, but the AI "assistant" clearly doesn't know what to do with this one, and I've exhausted the troubleshooting guides.

I've used xfinity for years and always been happy with the service.  Still am, for 11 minutes and 58 seconds out of every 12 minutes.  But the 2 seconds of rage is getting old.

Thank you for your time.