Anyone know how to get NAT from moderate to open on sky router?

Hi, my son's Xbox One suddenly seems to be behind a moderate NAT type, we're on Sky fibre and I have tried following this guide but it hasn't worked. forums.xbox.com/xbo…spx. Anyone any ideas why this should have suddenly happened and more importantly, how can I get his NAT type to open?

Really appreciate any help with this, he can't chat or join any multiplayer games at the moment.