ios app flow is missing view Controller in Flow. Xcode 6.1

Following is my application flow.

Flow 1) app Delegate - app login page(signup) -> Form View to -> welcome screen (on ok) -> Dashboard/User home page.

Flow 2) app Delegate - app login page(login) -> Dashboard/User home page.

I unchecked "Use Size Classes" from "File Inspector". I am not using autolayout. I am using different storyboard for different device like iPhone 6 , iPhone 6plus , iPhone 5s, iPhone 4s.

Now each time I'm checking the device, the app is running and loading the specific storyboard.

The app is running fine for only one iphone 6 plus device and iphone 4s,5s simulator.

But when I installed and tested it on multiple devices (all 4s,5s,6, another 6s device ) it is not loading the dashboard on welcome screen (on ok) in first Flow 1. and also on successful login in Flow 2.

All the devices having ios 8 and above.

I debugged the flow through code step by step. But it is following the right logical path.

Please if you have any solution help me with this situation. any suggestions are really appreciated.

Thanks,