"Apple told the dev community that they would be dropping support for IPv4 in 2016. In December, they disabled IPv4 literal translation to IPv6 addresses worldwide. This only affected carriers who ran pure IPv6 networks vs IPv4/IPv6 dual stack networks. In the US, T-Mobile is the only carrier not to have a landline business, so we did not have a large pool of IPv4 addresses, so we were a huge early adopter of IPv6 and never put in a dual stack. Our devices all have had IPv4 literal translation since the begining of LTE.
Apple wants to speed up the death of IPv4, so they made a change. T-Mobile pushed back, and eventually they turned it back on a few months back, but let the carriers know they were going to disable it again in the next iOS update.
So here we are. Nothing is "broken" on Apple's side, nor on T-Mobile's side. If your app is not working, it is because the app developer used an IPv4 literal; for example, they hard coded an IPv4 address into their app vs using a fully qualified domain name. This is extremely poor programming practice, and against Apple's developer policies... so Apple's official answer is "Update your app".
The only big carrier in the US that is affected is T-Mobile, because T-Mobile does not run an dual stack network. It sucks, because T-Mobile has been the most progressive major ISP pushing for IPv6, and Apple is punshing T-Mobile for that."