Guideline 2.1 - Performance - App Completeness
We still discovered one or more bugs in your app when reviewed on iPhone running iOS 11.2.5 on Wi-Fi connected to an IPv6 network.
Specifically, we received a network error message after we logged in the app.
Please see attached screenshots for details.
To resolve this issue, please run your app on a device to identify any issues, then revise and resubmit your app for review.
If we misunderstood the intended behavior of your app, please reply to this message in Resolution Center to provide information on how these features were intended to work.
For new apps, uninstall all previous versions of your app from a device, then install and follow the steps to reproduce the issue. For updates, install the new version as an update to the previous version, then follow the steps to reproduce the issue.
For information about testing your app and preparing it for review, please see Technical Note TN2431: App Testing Guide.
For a networking overview, please review About Networking. For a more specific overview of App Review’s IPv6 requirements, please review the IPv6 and App Review discussion on the Apple Developer Forum