I must admit then when we were with Sky using their hub I had 1 Xbox One connected all of the time and on occasion had 2 Xbox One's connected at the same time with no issues, however no ports were ever forwarded and only connected via Ethernet.
We recently came across to PN and also use a Hub One. Again 1 is connected all of the time via Ethernet and since before Christmas there has been only two issues with the NAT. As I always do, I let UPnP do it's job rather than forwarding any ports. Depending on your set up (wired or WiFi?) you could try the following to see if it cures your NAT -
1) When the error comes up, power the Xbox down completely, disconnect the Ethernet, power it back up, connect the Ethernet and test the connection and then see if your NAT is open.
2) If it's still not, leave the Xbox on but turn the hub off at the mains (or the switch on the back), wait a few mins and switch the Hub back on. Wait until it's settled and then see if your NAT is open. Do not keep turning the Hub on and off when trying to correct your Nat type. If it's still not open then without turning the hub off power the Xbox off as per 1).
If you connect over WiFi
3) Split the 2.4Ghz and 5Ghz via the hub manager, name the 5Ghz differently (simply add 5Ghz to your SSID) and see if your Xbox can see both SSID's. If it can but your Xbox is some distance from the Hub then connect to the 2.4Ghz SSID. If your Xbox is almost sitting on the Hub then go for the 5Ghz. Then repeat 1) (obviously missing the Ethernet bit out) or 2).
Again just to point out, UPnP is allowed to do it's job and no ports are forwarded. However you may need to forward ports if the game requires you to do so - GTA, Minecraft and some other new(ish) titles all work here:)
