I am convinced this is an xFinity issue as these problems started on various dates and times during the month of June coupled with the fact that our backups and access to software updates were previously working.
Being in the IT industry for 30+ years I go by the adage "what was the last thing that was changed before the problem started". The smoking gun points to xFinity.
The common thread is our iCloud backups worked prior to June before the problems started and I am convinced xFinity pushed a firmware update to the XB series routers during the month of June that broke the iCloud link. Additionally most of us confirmed the problem does not occur when we use a different service provider network along with taking our IOS devices to local Apple stores where the iCloud backups work instantly. I recently backup my iPad on my work Wifi and downloaded the latest IOS patch 16.5.1c with no issues. Given what we pay xFinity on a monthly basis for their service this is inexcusable to its customers.