Why don't you guys just optimize the app for iOS 10 and later? While doing so, you can more easily ensure that the app is fully and properly optimized for iOS. Users should update anyway to ensure stability and bug fixes on their iphones. Iphone 5 and later support ios 10 so user accessibility should still be there anyway. Iphone 4s half supports 10. Sounds like you may also be having problems on the server side of things as well though? I sorta work with this stuff everyday.