Hi Kevin,
The app crashes for some onknow reason. You can access the logs via debugging. That might give us an hint why
If the apps starts use: https://docs.mendix.com/howto/mobile/native-debug#1-introduction
On iOS: If the app does not start you have to use Xcode to connect to your device for and launch it from Xcode and start debugging
(For Android use Android Studio)
Cheers, Andries