Appbarbutton lost function after changing it's icon and label in UWP C# project

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C#

Windows

XAML

UWP

Win10

AppBarButton lost function (doesn't execute it's code) after changing it's Label and Icon (the code work only for first click on button but doesn't work any more(after the change)) for example :

In this code mediaPlayer.Pause(); works

private async void AppBarButton_Click_1(object sender, RoutedEventArgs e)
{
   //PPB.Icon = new SymbolIcon(Symbol.Play);
   //PPB.Label = "Preview";
   mediaPlayer.Pause(); //(i tested many other codes also)
}

but in this code mediaPlayer.Pause(); not

private async void AppBarButton_Click_1(object sender, RoutedEventArgs e)
{
   PPB.Icon = new SymbolIcon(Symbol.Play);
   PPB.Label = "Preview";
   mediaPlayer.Pause();
}

What I have tried:

I didn't have tried anything else