Universal Windows app crashes without an exception?

I have an app that currently crashes sometimes when attempting to do an in-app-purchase on Windows Phone 10. It seems to crash without throwing an exception. I am thinking maybe another thread is crashing the app? However it does not appear that the App's UnhandledException event is dispatching.

• This crashes about 5 seconds into running RequestProductPurchaseAsync(sku).
• It does not crash if the debugger is attached. (This confuses me.)
• The log before RequestProductPurchaseAsync(sku) is displayed and written to disk.
• I never see the log in OnUnhandledException.

await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () =>
    {
        try {
            if (IsSimulation) {
                purchaseResult = await CurrentAppSimulator.RequestProductPurchaseAsync(sku);
            }
            else {
                Debug.Log("PurchaseProductAsync is attempting REAL PURCHASE NOW!");
                // Crash ~5 seconds into this call. No exception is thrown.
                purchaseResult = await CurrentApp.RequestProductPurchaseAsync(sku);
                //  This does not display.
                Debug.Log("PurchaseProductAsync got result " + (purchaseResult == null ? "null" : purchaseResult.Status.ToString()));
            }
        }
        catch (Exception purchaseExc) {
            purchaseResult = null;
            result.ErrorCode = "-285";
            result.ErrorException = purchaseExc;
            result.ErrorMessage = "Exceptional Error";
            Debug.Log("PurchaseProductAsync got an exception when attempting to purchase from CurrentApp or CurrentAppSimulator. " + purchaseExc.GetType() + ": " + purchaseExc.Message);
        }
    });

Any ideas on how I can capture or debug this crash?

public App()
{
    this.InitializeComponent();
    appCallbacks = new AppCallbacks();
    UnhandledException += OnUnhandledException;
}

private void OnUnhandledException(object sender, UnhandledExceptionEventArgs e)
{
    // Never seems to run
    Debug.Log("Received unhandled exception");
}