How do I address React Native running poorly on physical iOS device vs Simulator?

I've recently finished building an app using React Native, and I'm in the process of shaking out the last remaining bugs. While the app performs exactly as it should in Simulator (compiled in Xcode using the release settings), on my physical iOS device it's ridden with subtle layout bugs and rendering problems. Calls to setState() appear to be failing after certain events, for example, when I make a call to fetch() I set an item in state to show a loading image just before the call, when the response is received state is changed to restore the previous image. On Simulator this works fine, on the physical device it correctly changes to the loading icon but fails to switch back. As far as I'm aware, there's no differences in the build between Simulator and the physical device, so what's the likely culprit?