xfinity stream: unable to watch shows when connected to home WiFi

The wife and I are both unable watch live tv or recoded shows using the xfinity stream app on our devices when connected to our home WiFi, which is through Comcast using the latest xfinity WiFi tower. The app opens as normal, however the home screen just shows blank thumbnails/windows where the picture of the show should be. We can pick a channel to watch, click “watch”, and the viewing window will pop up and act like it’s connecting or loading but the show never starts. Just the three dots rolling across the screen. What is really strange is that we have no problems using the app to watch shows when we turn WiFi OFF and use cellular data. The app even worked for my wife when she connected using the WiFi at her doctors office. Now I don’t know if they have xfinity internet or not but I’m kind of at a loss. The Comcast help line has not been able to help after two hours on the phone. Anybody have any ideas why we might be having these problems?