A while after I deploy my code to iOS the phone hangs up - xamarin

Question

Is there some way I can track what's happening with Xamarin? I do a debug with a target of my phone and then later it hangs up. I can't do anything, can't shut it down with the button on the side and the only way I can get the phone to work again is by pressing the button on the side and the home button. Running on iPhone 6s Plus.
Here is some code that I suspect might be causing a problem. Would also like to know if anyone can see anything that might cause the problem with the code:
public partial class App : Application
{
public static DataManager db;
private static Stopwatch stopWatch = new Stopwatch();
private const int defaultTimespan = 1;
public App()
{
InitializeComponent();
}
public static DataManager DB
{
get
{
if (db == null)
{
db = new DataManager();
}
return db;
}
}
protected override void OnStart()
{
App.DB.InitData();
MainPage = new Japanese.MainPage();
if (!stopWatch.IsRunning)
stopWatch.Start();
Device.StartTimer(new TimeSpan(0, 0, 1), () =>
{
if (stopWatch.IsRunning && stopWatch.Elapsed.Minutes >= defaultTimespan)
{
Debug.WriteLine("Checking database");
PointChecker.CheckScore();
stopWatch.Restart();
}
return true;
});
}
protected override void OnSleep()
{
Debug.WriteLine("OnSleep");
stopWatch.Reset();
}
protected override void OnResume()
{
Debug.WriteLine("OnResume");
// deductPoints();
stopWatch.Start();
}
}

Answer 1

iOS requires that everything is setup, with 17 seconds, on the initial first load. This means that you must set the MainPage in your App constructor, you can't set it in OnStart.
Or, you can place MainPage = new ContentPage(); in your App constructor, then it will be replaced in OnStart. However, you must set the MainPage, when it's constructing the Application.
Android and UWP I think, give you some freedom, and you can set it in OnStart, but definitely not iOS.

Answer 2

My iPhones are hangs up when I have debugger connected to running app and that connection is interrupted. For example, if you unplug lightning cable while Visual Studio is debugging - the phone will hangs.
So try to start your application from phone(without debugger attached) and check your datacable.