XBOX OS FORCING UPNP WHEN CONSOLE IS IN THE DMZ

I've just found this on Reddit and read the quotes from the Xbox Engineer who started this post:

https://www.reddit.com/r/xboxone/comments/5og87g/psa_networking_info_part_2_nat_dns_upnp_wtf/

There's something not quite right with Ethernet connections in regards to Xbox OS since the last updates.

I've got a similar issue with my One X that the OS keeps forcing UPNP when my Xbox One X is in the DMZ with a static IP setup, so in theory this should not been happening, but it is???

I will get maybe 5 times at most connected to Live perfectly then it will go into some kind of semi connected state stating moderate NAT & UPNP not successful or a Teredo warning message blah blah blah, it just repeats itself over and over, again this should
not be happening period if my One X is in the DMZ as all ports are open.

Rebooting both router and Xbox doesn't solve the issue.

It's also negotiating when I look up my network stats with a stated connection speed of 10 mbps when it should be at 1000 mbps?, it's extremely slow at refreshing the network stats and overall usage making it almost unusable.

It was a right mission to just get it to update after I'd reset back to factory settings both fully and partially.

I've got a lot of networking experience and I've tried every type of connection setup both dynamic and static, UPNP, DMZ, with firewall on/off, full cone NAT, all ALG off, DHCP disabled on the router, both automatic and manual configurations on the One X
etc etc, pretty much everything you can think of far and beyond what a normal end user would do in this situation.

Powering off everything over night to get another Dynamic IP from my ISP (Telia Finland Oyj) which doesn't offer IPV6 at the current time, but nothing seems to solve this riddle and further to add there is no Double NAT at play as I've used an ASUS AC68U
with the same DMZ / Static IP setup and that worked fine, sadly that died after 7 months so I moved onto a TP-Link VR600 V2 Archer.

I've had other similar issues with other router / gateways made by Netgear, Bewan, Cisco and Asus before but this really is a conundrum with this TP-Link VR600 V2 Archer.

My laptop with Windows 10 works perfect in every ethernet port I have on my VR600 V2 Archer so it cannot be a router issue as it's working as intended, it's updated to the latest firmware so it seems the issue is related to be the One X or Xbox OS itself,
being based on Windows 10 kernel it's also strange my laptop works but my Xbox doesn't?????

I'm debating whether to send it in but since reading another post on Reddit from someone who has had a similar experience to mine it appears this is an issue that does not seem to go away even with different consoles being replaced or refurbished so it might
be a firmware / software issue within the Xbox OS itself.

Further to add I've also got a slight loud buzzing coming from the console which indicates some form of coil whine or possibly be hard drive related but I'm not overly worried about that right now as I run my games off a Samsung T5 SSD for improved performance
anyhow.

If anybody else on here from the Xbox support or the Xbox engineering team can advise further then please feel free to help and reply as I think this issue will become more mainstream as time goes by if it is indeed OS related.

:)