From Apple

2.1.0 - App Completeness

Performance - 2.1

We discovered one or more bugs in your app when reviewed on iPhone running iOS 9.3.2 on Wi-Fi.

We were unable to log in because the log in button is not responsive.

We've attached screenshot(s) for your reference.

Next Steps

Please run your app on a device to identify the issue(s), then revise and resubmit your app for review.

Apps are reviewed on an IPv6 network. Please ensure that your app supports IPv6 networks, as IPv6 compatibility is required.

For additional information about supporting IPv6 Networks, please refer to Supporting IPv6 DNS64/NAT64 Networks.

For a networking overview, see About Networking.

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(s). For updates, install the new version as an update to the previous version, then follow the steps to reproduce the issue(s).

Resources

If you have difficulty reproducing a reported issue, please try testing the workflow described in Technical Q&A QA1764: How to reproduce bugs reported against App Store submissions.

If you have code-level questions after utilizing the above resources, you may wish to consult with Apple Developer Technical Support. When the DTS engineer follows up with you, please be ready to provide:

complete details of your rejection issue(s)

screenshots

steps to reproduce the issue(s)

symbolicated crash logs - if your issue results in a crash log