It's not an isolated issue, seems other ISP's are struggling with this service also, if this poll is correct: XBOX Cloud performance
The Xbox Cloud streaming is still in Beta stage. I am thinking this might be a protocol issue, although I am not sure what protocol it actually uses. Typically certain protocols receive priority over other less critical protocols, to ensure smooth performance.
With a streaming service like this ping times and bandwidth availability would be required for a smooth experience.
So I am thinking the protocol is not being prioritized properly by ISP's yet. Another possibility could be poor routing.
It's hard to say, but apparently if you bypass the home hub completely the problem goes away. So it could be an issue related to the build in firewall. You can try disabling it to see if that makes a difference, just for testing purposes. Or use ADMZ to grab a public IP and see what effect that has on the performance.
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