App not approved for issue that we cannot replicate!

Hello, we are submitting an app and using the Amazon Web App Tester to test all issues, but we are not able to re-create the issue! Case 133733011 Steps to reproduce : 1) Install the App . 2) Launch the App . 3) The app asks for log in on Facebook and directs to a web browser but doesn't return back to the app . We have tried this on a brand new Kindle Fire and also on a new Note 3 and each time we are not able to replicate the issue. I am lost on how to fix this without actually experiencing the issue. Any help or insight would be much appreciated. thank you, Chris

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