The NAT type on my Xbox One changes to strict whenever I turn it off or put it in sleep mode. If I clear the cache and reset my router it goes back to open, but it's a giant pain to do that every time I want to play a game. I use my own router with the ISPs modem, so I have the router in access point mode. Some of the time, when I get the strict NAT type the Xbox says UPnP unsuccessful. From what little I've figured out UPnP is a setting on the router that's greyed out when in access point mode. I would ask my ISP about this, but their support is terrible.