Hrm, did you try resetting the xbox as described in the article I mentioned in my last post to get it to perform upnp? When doing this, make sure you reboot your modem just prior to doing this on the Xbox.
The only other thing I can even think of suggesting is disabling IPv6, and manually set an IPv4 address on your Xbox One that will work with your local network...
I see it's your first post here, so welcome to the community! Did you catch C0RR0SIVE's posts earlier in this thread? He has some good explanations and things to try. Good luck!