App not compatible on iPhone 4s and 5 in Testflight

Question

I'm nearly finished with my app, and I'm testflighting it right now. The problem is that I can't get it to work on iPhone 4s and iPhone 5. The deployment target is set to 8.0, and it's running perfectly on the iPhone 4s simulator. When my testers open TestFlight, they can see this list of compatible devices, and people with devices older than iPhone 5s can't install it. This is what my testers see in TestFlight:

Another strange thing is that it compatible with iPad, but I've set my devices to iPhone only in Xcode.

I have tried researching this, but I can only find questions related to auto layout and sizing issues. I've made sure everything should look fine on all devices, what am I missing?

Answer 1

The problem was a pretty easy one to solve, thanks to rmaddy for pointing it out. I had to set Built Active Architecture Only in Build settings to No for release. I didn't change the setting for debug as that only gave me compilation errors. See screenshot:

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