app failing to load for a single user

Hi,

We have been developing an app and have recently started alpha testing. Most of our testers are in the UK and the app has been running fine, however we have one tester in Bahrain who's app seems to stay on the loading screen (3 white dots) and it never reaches the games splash screen. Eventually they just close it because nothing happens.

We have been trying to work out why without much success. We are waiting on some diagnostics and some tests like whether or not other apps work and finding out whether the OS is up to date but we are sort of out of ideas as we dont have access to the headset. 

They have tried factory resetting and using different users and we have uploaded newer builds that still dont work on their device.

Does anyone know what might be happening? Why might only one tester have issues with the app never loading? We were trying to work out if there might be regional issues but we cannot find anything online that would suggest that apps are only available in certain countries, and there dont seem to be any settings in the developer portal for what countries it is available in.

Thanks for any help,

Elliot