Have you ever gotten this message from App Review?
Performance – 2.1
We were unable to review your app as it crashed on launch. We have attached detailed crash logs to help troubleshoot this issue.Next Steps
Please revise your app and test it on a device while connected to an IPv6 network (all apps must support IPv6) to ensure it will launch without crashing.
The App Review Team regularly rejects apps that fail on IPv6 networks. Some of the time this feedback is a false positive. The app may have crashed for reasons unrelated to networking, but because it happened to crash while connected to an IPv6 network this is the feedback you receive. It is up to you to diagnose the source of the crash.
Some of the third party libraries you are using may not be compatible with IPv6 networks. For example, some analytics companies have provided SDKs in the past which crash randomly on IPv6 networks.
Another common culprit is any of the “reachability” libraries out there. The problem is not always the library itself but how it is used – your app should not try to check for network availability before a network request, and it should not use IP addresses.
So how do you test on an IPv6 network?