Xamarin Forms Android Webview Refresh not working

Question

I'm currently developing a little app which uses the Android WebView to display a specific website. Nothing big or special. But I created a menu where you can set the url to the website. After saving the url and getting back to the webview I can't refresh the webview. Only when I restart the app the new url got loaded. I don't know what I'm doing wrong...

WebView.xaml:

<ContentPage.BindingContext>
        <viewModels:WebviewViewModel />
    </ContentPage.BindingContext>

    <ContentPage.ToolbarItems>
        <ToolbarItem Text="reload"
                 Command="{Binding ReloadWebview}"
                 CommandParameter="{Binding Source={x:Reference webView}}"
                 Order="Primary"
                 Priority="0" />
    </ContentPage.ToolbarItems>

    <WebView x:Name="webView" Source="{Binding Url}" /> 

Webview.xaml.cs:

public partial class Webview : ContentPage
    {
        WebviewViewModel webviewVM;

        public Webview()
        {
            InitializeComponent();

            webviewVM = new WebviewViewModel();
        } 
...

protected async override void OnAppearing()
        {
            base.OnAppearing();

            this.SetUrlAsSource();

            webviewVM.ReloadWebview.Execute(webView);
            webView.Reload();
            ...
        }

private void SetUrlAsSource()
        {
            try
            {
                webView.Source = SecureStorage.GetAsync(Constants.SourceUrl).Result;
            }
            catch (Exception ex)
            {
                Debug.WriteLine($"Exception: {ex.Message}, {ex.InnerException}, {ex.Data}");
            }
        }
}

WebViewViewModel:

class WebviewViewModel : BaseViewModel
    {
        private string _url;

        public WebviewViewModel()
        {
            Url = SecureStorage.GetAsync(Constants.SourceUrl).Result;

            ReloadWebview = new Command<WebView>((key) =>
            {
                key.Reload();
            });
        }

        public string Url
        {
            get { return this._url = SecureStorage.GetAsync(Constants.SourceUrl).Result; }
            set
            {
                if (this._url == value)
                {
                    return;
                }

                this._url = value;
                SecureStorage.SetAsync(Constants.SourceUrl, this._url);
                OnPropertyChanged();
            }
        }

        public ICommand ReloadWebview { get; }
    }

Thanks in advance