OK, we have found the issue. Gretsche was incredibly helpful, making it easy for us to figure it out.
Just a little basic explanation first. Typically, each of your devices gets a private ip address on your network from your router (DHCP server), and your router presents a single public IP address to the internet covering all of your devices.
So lots of private ips - one for each device - and one public ip address. Getting this information allows us to figure out who has what and then make myantipodes.com and the myantipodes page work.
Things changed with ipv6. ipv6 is just a way to provide more ip addresses to the world because it was running out of ipv4 addresses. But we don’t have that problem in NZ and so no ipv6, and our only real world experience with ipv6 is through our overseas users.
What we have found is that some routers present multiple public ipv6 addresses to the internet - as opposed to just the one. So the code we use to make sense of which devices relate to which other device, etc needs a change to cope with this.
As mentioned, we have just six users with this problem but it could eventually expand to many more. We have now written the new code and we will test it here. But we will need to get into one of the problem devices to properly test it. It is 2am where Gretsche is so we can’t do that test right now for him but we will hopefully find another ‘guinea pig’ soon and report back.