Unicast maintenance problem

I have a brand new SB6190 Arris modem. I attached it to a Google nest/Google Wi-Fi set up. Occasionally, things are just dropping out. I checked the various power settings from the configuration screen on the modem, and upload power is low. Comcast was going to come out, I guess check the power outside. But it's not hard, so they didn't. Then tonight, a new development. I looked at the log after service dropped, and there is a page of errors with comments about "unicast" problems and "ranging" issues and so forth. I've chatted with Arris, they said it's definitely a Xfinity/Comcast problem. I've had technicians out at the house multiple times, inside and outside. Nobody seems to be fixing the problem. I saw a thread about old inside wiring. Apparently, I do have old wiring, but when they checked it, it was apparently fine. Does anyone have any suggestions? I'm reluctant to set up another Comcast visit when they just keep coming and saying everything is OK, when the error log says otherwise.