What 's wrong with my environment IPV6 for ios?

I submitted my first iOS app to Apple Store and the review team has rejected me because:

Your app crashes on iPad and iPhone running iOS 9.3.4 connected to an IPv6 network

My problem is that I can not reproduce the error.

I have a iPhone 5 (iOS 9.3.4) and the environment as shown in the screenshots.

Is my iPhone5 working in IPv6?

Solution

I fix my issue. There was an error on my web service server (1&1).

But I never did my application to fail in my test environment. I think it was well set up from the beginning, but no one could confirm.

Thanks for help!