They Broke It
This worked well most of the time, until the last update. Now in-home playback of recorded shows frequently returns an "8001 Error", whatever that is. And refuses to play back any recorded shows on any mobile device. Oddly, playback is possible through the XFinity website through a laptop, but that really defeats the purpose of having an app.
wallemon about
Xfinity Stream, v4.3.0