Not able to stream Space City Home Network while on home network

For anybody following along with a similar issue:
This was resolved with help from Xfinity support.  They were able to determine that my cloud DVR storage was full and that was causing several issues:
No recent DVR recording were available in the Stream app, even though they were available on the cable box.

Only a sub-set of the channel lineup was available in the Live-TV channel list.

Some content was not available when selected from the Watch Now page, like NCAA Tournament games.

There were no errors or warnings in the app.

The cable box showed less than 50% usage in the DVR space.

The cloud DVR storage space is much smaller than the space available on the cable box.

My cable box had recently filled up to over 95% capacity, but was currently below 50%.

To resolve the issue, I deleted almost all of the DVR recordings from the App.  I also used the Sync DVR function on the cable box, under the Settings > Device Settings menu.

After deleting the DVR recordings, I signed out of the app and waited several hours.  When I checked back later, I was able to use the app without any issues.

There were also many sign-out and sign-ins, account refreshes, channel line-up refreshes, and re-installs of the Stream app, but I don’t know if any of that was actually necessary.