I get a "Double NAT detected" massage in Xbox whenever I turn my console on. and I can't play multiplayer.

But when I run "Check NAT" on the console, I usually get a "Your NAT is open". then I'm able to play multiplayer.

So why don't I get a NAT type is open from the start? I have to do it every time I turn the console on!

Also, I can't connect my router with an Ethernet cable to the console cuz if I do the double NAT never goes away until I go wireless.

I have port forwarded the Xbox ports. my Upnp is active.