Can't get support for an issue that is clearly outside the house - external upstream ingress or a grounding failure maybe?

I've been having network issues with my Xfinity account for well over a year now. I occasionally work from home, so dropped zoom/teams calls is a real problem! I've done every diagnostic that I know to do, bought a new modem (Arris), run an entirely new line from the connection that comes from the box on the pole in the back of the house with no splitters or connectors (looks ugly, but I was desperate), tested out attenuators/FPAs to get all of my dBs in line, and I now have a perfectly within spec connection: 

Physical RF Signal Levels
Downstream Power: -1.9 to +1.5 dBmV, most very close to 0 (Ideal range is -7 to +7 dBmV)
Downstream SNR: 38.6 to 40.9 dB (Ideal range is >35 dB) 
Upstream Power: 40.3 to 41.5 dBmV (Ideal range is 38 to 48 dBmV)

However, I am still getting drops. My error messages are textbook 'outside the house' type problems, especially given the above specs:

Critical Modem Event Logs
No Ranging Response received - T3 time-out; CM-MAC=f8:xxxx; CMTS-MAC=00:xxxx...
CM-STATUS message sent. Event Type Code: 2; Chan ID: 4...
SYNC Timing Synchronization failure - Loss of Sync... (etc.)

Moreover, while there can be a little bit of randomness with the timing, a lot of the issues seem to happen at around the same time of the day in the morning and early evening - that feels like it totally fits interference timing patterns. 

I say all of this to the Xfinity rep, and then to the person to whom they escalate it (when I can get them to do that), and I still can't get an informed Line/Network Maintenance Technician to come out, or check the neighborhood logs, or even get that I am having an issue with the CMTS failing to respond to my modem's ranging requests at specific times.

I've seen some other folks get help from knowledgeable xfinity employees (and awesome community members here), so I'm hoping I can get help too.