I've been having the same issue with my Xbox for a while now. Today I was trying to figure it out and might have stumbled on to something. If you go to network settings on your Xbox and select advance settings and go to port selection and choose manual, then select one of the ports, it might open for you. You might have to try several different ports until it works but I got both my son's and my Xbox to show open. I think it really did work. Lets see how long it last.
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