You are not alone. The exact same issue has been happening to me since January - when there would transient drops in Downstream power, with a drop in SNR values sometime between 3 pm - 9 pm (I happen to be an engineer/scientist). The modem would then lose the connection and stay that way for at least a few minutes - ruining the work I often do from home (esp. these days).
When the first tech came out, he couldn't find any problem because it didn't happen while he was here at his pre-appointed time. I explained and showed the modem logs showing the downstream signal drop in a transient manner - at which point he started being politely condescending - and in the end just ignored the problem and went away.
I complained again, and the second tech came to say people were outside working on comcast's lines external to my home, which should fix the problem. Then he came into my home to check my wiring "Just in case". He then went away saying the external work should fix the problem with Comcast's infrastructure. It didn't.
I later found that Comcast charged me $70 for the second tech visit, because "there was a problem inside my home". I was apalled and had to call them to reverse the charge. The problem remains, of course, very much with Comcast, one and a half month later.
I'm certainly hoping that if nothing, this 5G hype will let me have a wireless broadband, so that I can rid myself of Comcast. That remains my only hope.
