WiFi connectivity problems

We have been experiencing WiFi connectivity problems ever since our cable was replaced in March, following a tree strike. Cable TV, VOIP, and sometimes one or two wifi devices work but more generally not. My latest call last evening ended with the technician acknowledging that he would need to connect to the gateway's diagnostics. His promised return call did not happen.

The easiest way I use to show the problem  is the Xfinity app on my Samsung S21. When I select 'Run a Test' , the app soon tells me there are no outages, measures a gateway connection speed usually > 100% of plan, the proceeds to test connected devices. The results vary, from 'we've encountered an error, weak wifi, strong wifi, and unable to test. I've run a dozens of these tests and have screenshots. I replaced the modem last week. Each of the devices works well on our AT&T wifi.

The modem is a Technicolor CGM4331COM. I have found descriptions and product literature but nothing around troubleshooting yet IMy next technical step will be to connect via ethernet and look for help in the firmware interface.

This is a pretty miserable customer experience to date, with the only highlight being the prompt and courteous equipment swap at the local store.  Perhaps an excalation to level 2 will help, please just don't have a robot call me and insist on restarting the Gateway.