Xbox Live party chat and MTU problem

[Dubs]

Hi, i have been using Three 5g for a week now and while i am very pleased with my DL speeds, i cannot join people in xbox live party chat. The xbox says i have an mtu problem. I have tried port forwarding, putting my xbox in the dmz and turning off the firewall but nothing works.

[CSpec01]

I've tried this but sadly it only works within a few seconds of updating the router settings to UPnP enabled. Giving it some time and testing again shows the issue is still present. 

[DrGravity]

What firmware do you have on the router? You can see via the app or router settings and the version will end with bXX (where XX will be a number). I'll wager it's the latest b14 version.

The MTU issue has been present since last year and does impact gaming but it never prevented Xbox parties before in my experience. I've had the same problem recently since the router auto updated to the b14 firmware. It seems to have broken UPnP / port forwarding

[Dubs]

Hi mate, i have the ZTE MC801a and am on B15