Two Xboxes in same flat on same network have party chat issues

[Robocop41]

I’m in a flat share with some other people so we all share the same Sky broadband router.

When we play with others over the internet party chat works fine. When we try to add each other from the same house we can see the party chat overlay showing that someone is speaking but you never hear the chat.

This seems to be a known issue from a bit of googling as the same problem is reported in lots of posts with no solution:

https://answers.microsoft.com/en-us/xbox/forum/all/two-xbox-ones-in-the-same-house-chat-problem-2020...

https://answers.microsoft.com/en-us/xbox/forum/all/2-xbox-ones-in-same-network-no-chat/f981d7cb-29b0...

https://www.reddit.com/r/xboxone/s/oP4dSlsX1k

I have open NAT on both Xboxes, the party connects fine, nothing on mute and no restrictions.  I’ve tried numerous types of headset. We have different ports selected for each xbox. IPv6 is enabled. Is this simply not possible using a Sky broadband router?

anyone else using sky manage to get more than one Xbox working with party chat ok?

[mae-3]

@Robocop41 

Have you disabled UPnP on the Sky router and set the port for each differently?

[Robocop41]

Yep I tried manual ports for each Xbox and static IPs with UPnP off too. Even when I do use UPnP I can clearly see that each Xbox has a different manually assigned port and that the NAT type on both Xboxes is open. Just can't figure out why the chat is not working.