Comcast Wi-Fi-based 4K Cable Boxes Failing

Last week my only Comcast Wi-Fi-based 4K cable box (Xi6-A) started failing.  Home Wi-Fi is perfectly fine.

Replaced the Xi6-A with a brand new XiOne-SC (B) and exactly the same issues.

My guess is technical problems with any Wi-Fi access points EXCEPT Comcast's own Wi-Fi access points.

Comcast doesn't want you using your own network equipment and now their Wi-Fi only  cable boxes will start to fail.

I'm waiting to see if their "advanced" support has any ideas.