The 27.1 carrier update that came out with iOS 10.2 has broken the VPN on my iPhone 7. The VPN works on my iPhone 5S with 10.1.1 and the previous carrier update. Here are a couple of links to others having problems with other apps after the update:
Is T-Mobile aware of this and is a fix coming?
Best answer by ric_d
My VPN runs on an Amazon Web Services EC2 instance and right now AWS does not enable IPv6 for EC2. So it's really an Amazon issue. EC2 is supposed to have IPv6 support in 2017, so I'll just wait. Thanks for asking!