Try the TBS Live websites (where Channel gets it from) TBS East or TBS West and see if you can Sign in with Xfinity and watch it Live.
If not, it's an issue with the Xfinity auth servers, or it's not in your Xfinity package.
That's how TVE works w/Channels DVR. Has nothing to do w/Xfinity Stream or any app.
Here are some TVE Troubleshooting tips