App Store review , APP COMPLETENESS, Why app getting rejected with IPv6 message?

Hi,
I am using old unity version unity4.6.5f1.
And photon Unity Networking v1.64
Generated by Doxygen 1.8.7
Thu Nov 5 2015 15:48:10.

1. Submitted for review to app store.
2. It is rejected with the error "We discovered one or more bugs in your app when reviewed on iPad and iPhone running iOS 10.2 on Wi-Fi connected to an IPv6 network. Specifically, a network error occurs after launch."
3.Is it problem of PUN SDK ? or Problem of Unity version ?
4.How to check in IPV6 ?

Please elaborate.