App Rejected 3 Times, clueless how to fix issue
If Apple reject your app due to a technical problem, they usually provide a screenshot. Check the bottom of the message in iTunes Connect to see if there is an attachment.

You could try some severe logging: in the app, log exactly what is happening, all the inputs, all the errors, and have it report to your server. Thus, after they reject the app, you can go through the logs and see what is happening.