Hello lancastc and LoafAlot,
I apologize for any inconvenience this issue may have caused you. Windows Phones and Tablets are not currently supported. XFINITY TV Go is only supported on Mac and PC computers at this time. Although iPhone, iPad, Android, Linux and other devices may access XFINITY TV Go, they are not supported platforms and not all features/functions are guaranteed to work, including but not restricted to video playback.
Is there any update on this? I am on my second Surface Pro, and a frequent traveler. Would love to be able to use a real app to stream and download content for offline usage. Come on -- the market is certainly big enough for Win10 machines. What's the hold up?