This is a generic message Apple sends out when your app fails for any reason. They turn off IPv4 networking, run your app, if it dies/gives them a black screen, they assume you’re making IPv4 calls. I wish Apple would automatically provide you a console log run of the test device. Since iOS 10 has come around, the logs are polluted with other messages making your messages hard to find and follow.
That said, you can always ask them provide you with a console log from their test run and that might help you narrow down the problem.
What all real iOS devices did you test on?
Did you test using their testFlight system or just developer/adHoc builds?
Rob