iOS App Store ExecutionEngineException attempting

I have a really awkward problem. I have build my app for iOS and tested it on all emulators and it works fine. I have installed it on a device (iPhone 6 plus) and that works fine as well. However, when I submit it to the app store, the feedback is that it crashes on launch on all devices. The crash log attached shows this error;

Unhandled Exception:
    System.ExecutionEngineException: Attempting to JIT compile method 'GalaSoft.MvvmLight.Messaging.Messenger:get_Default ()' while running with --aot-only. See http://docs.xamarin.com/ios/about/limitations for more information.

The code that causes this error is in ViewWillAppear;

Messenger.Default.Register<LoggedInFailedMessage>(this, LoginFailed);
Messenger.Default.Register<LoggedInMessage>(this, LoggedIn);

The below stack overflow thread seems to indicate it might be caused by using value types, but I am using reference types.

System.ExecutionEngineException: Attempting to JIT compile method only in Debug Mode on device (MonoTouch)

Any ideas would be greatly appreciated! I don't know how I can test for these errors if they work when i debug on emulator and device but fail when apple test it.

Most of those issues where fixed a long time ago. Make sure your options for the AppStore builds (or the one you used to submit) match the one you're testing (e.g. Debug builds).

In particular make sure that the Enable generic value type sharing options is ON on the build you are submitting. This will include some extra code to ensure all value types code path variants are available at runtime.

Note that this setting should already be ON by default. Still it's a good practice to ensure your debugging/release settings are mostly (except debugging stuff) identical. Otherwise you risk testing different code, locally, than what you're submitting to the store.