I call BS on any fix that TPG has provided; none of these work and trying to get people to perform the same thing over and over again with the same results, well ... ... ... “Insanity is doing the same thing over and over again and expecting different results.”
The way I fixed it was by going out and buying a new router ... Which I shouldn't have to do because something that works on every other device normally takes 15 months (going by the original post) and no even acknowledgement of a problem. Even to the point of asking how often I reboot my router; how frequently should I be rebooting it? Every time I want to connect to Xbox Live? I think not. As soon as I turn on the xbox now with the new router, plugged in via ethernet. Wow, it works straight away.
This is clearly an issue with the devices you provided; clearly shown by the amount of people who have come to this thread.
I just got TPG NBN a couple of days ago and have the same Xbox One issues as the previous posters. When connected by wired connection to my new tplink router my Xbox live is no-go. However I also find my PC won't connect to the router, it says "cable unplugged", but if I move the same cable to my old adsl router it connects and gets an ip address (but no internet as the adsl has been turned off), so no problem with the cable or PC. Neither of these devices have fixed IPs at the moment.
From previous posts I imagine wifi would work but I don't want this as games that require stable low latency etc do not play as well over wifi.
It also looks like at present there is no solution other than ditching the router. Luckily I didn't get a fixed term contract with TPG NBN, I've been happy with TPG for 18 years(!) but I will regretfully have to try another provider if I can't resolve these problems. I don't want to but I'm not getting what I need, and from previous posts here I better not hold my breath for a fix.