Tested a little further. The Comcast menus indicated Wi-Fi signal was weak getting to the unit, even though there was only one wall and about 20 feet separating it from the gateway. I moved the Wi-Fi access point around to see if I could improve the signal to it, and there was no help, even when I moved the WAP outside.

Only when I opened the plastic door and dangled the box below the TV did the signal improve. Thinking that the screen might be an obstruction to Wi-Fi, I added an access point in the room behind the TV, so Wi-Fi only had to go through the plastic flapper door. It did not show a signal improvement, and tonight the client indicates it is still acting up.

The Comcast tech had encouraged me early on to get a new box. I guess that is next.