I'm living here in the future compared to this post, but I had the same symptoms:
- Roku not working with Xfinity Stream Beta App, error 500
- iPad not working with Xfinity Stream iOS App, just ... hangs ... ... ... over and over
What did work for me to restore to Roku and iPad. In my case, I have my own modem and separate router. It seems the original poster had a combo modem / router; I don't know if this is why my solution - inspired by @shermintoga 's original - is slightly different (I didn't have to disconnect the coax).
- Disconnect power from Cable Modem (My own modem, not Xfinity Equipment)
- Disconnect power from Router (Google Nest Wifi)
- Wait 60 seconds, apply power to Modem.
- Wait for Modem to show that it's completely back online
- Apply power to Router
Boom! Back in business.
What had not worked:
- Multiple factory resets
- Multiple power on/ off cycles
- Multiple re-installations of the xfinity stream beta app (roku only)
- "Updating" the xfinity app in-place on the roku
Hope this helps someone in the future.