Xamarin button visible in iOS simulator but not on device

Question

I'm new to Xamarin but know some iOS, got someone else's code dumped in my lap to fix some bugs. I've googled quite a bit, but I can't solve this one.

Everything works fine deployed on Android, deployed on iPhone 4/iOS 7.1.2, and simulated as iPhone 6/iOS 9.3 in the iOS simulator.

Problem

The btnNews button is visible in the iOS simulator (iPhone 6/iOS 9.3) but not when the code is deployed to an iPhone 6/iOS 9.3.1.

MainPage.xaml in a portable project

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:c="clr-namespace:Cookies;assembly=Cookies"
             x:Class="MyCompany.MainPage" Title="MyCompany">
  <Grid ColumnSpacing="1" RowSpacing="0">
    <Grid.RowDefinitions>
      <RowDefinition Height="*" />
      <RowDefinition Height="50" x:Name ="buttonsRow"/>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="*"/>
      <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <c:CookieWebView x:Name="webView" Grid.Row="0" Grid.ColumnSpan="2">
    </c:CookieWebView>
    <ActivityIndicator x:Name="activityIndicator"
          VerticalOptions="FillAndExpand" HorizontalOptions="Center" Grid.Row="0" Grid.ColumnSpan="2" />
    <Button x:Name="btnNews" Text="back to news list" BackgroundColor="#E15F59" BorderRadius="0" BorderColor="#E15F59"
            TextColor="White" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" BorderWidth="0" IsVisible="False"
            HorizontalOptions="FillAndExpand"/>
  </Grid>
</ContentPage>

MainPage.xaml.cs MainPage()

namespace MyCompany
{
    public partial class MainPage : ContentPage
    {
        private Button _btnNews;
        private ActivityIndicator Loader { get; set; }
        private RowDefinition _row;

        public const string URL_NEWS = "http://www.mycompany.com/";
        public const string QUERY = "master=app";
        public static CookieWebView WebView;
        public static string CurrentUrl;
        bool externalUrlClicked = false;

        public MainPage(string url = null)
        {
            InitializeComponent();

            // cookies common : https://github.com/seansparkman/CookiesWebView + nuget package CookiesWebView nuget : https://www.nuget.org/packages/CookieWebView/1.0.0
            // ios: http://stackoverflow.com/questions/29768019/cookies-in-web-view-xamarin-ios

            NavigationPage.SetHasNavigationBar(this, false);

            WebView = this.FindByName<CookieWebView>("webView");
            _row = this.FindByName<RowDefinition>("buttonsRow");
            Loader = this.FindByName<ActivityIndicator>("activityIndicator");

            WebView.Navigated += _webView_Navigated;
            WebView.Navigating += WebView_Navigating;

            var source = new UrlWebViewSource();
            source.Url = GetUrl(!string.IsNullOrEmpty(url) ? url : URL_NEWS);
            WebView.Source = source;

            ReadCookiesFromSettings();

            _btnNews = this.FindByName<Button>("btnNews");
            _btnNews.Clicked += _btnNews_Clicked;

            // Keep free from iPhone status bar
            this.Padding = new Thickness(0, Device.OnPlatform(20, 0, 0), 0, 0);
        }
    }
}

MainPage.xaml.cs _webView_Navigated()

This method runs whenever a link is clicked in the web view. If the url is a "news item page" then btnNews ("Back to news list") should be shown, else btnNews should be hidden. I have set breakpoints to validate that the correct if/else blocks run at appropriate times. The deployed app uses the same urls/web content as the simulated app.

public void _webView_Navigated(object sender, CookieNavigatedEventArgs args)
{
    if (externalUrlClicked)
    {
        args.Url = CurrentUrl;
        externalUrlClicked = false;

        return;
    }
    else
        CurrentUrl = args.Url;

    if (args.Url != GetUrl(URL_NEWS))
    {
        _row.Height = 50;
        _btnNews.IsVisible = true;
    }
    else
    {
        _row.Height = 0;
        _btnNews.IsVisible = false;
    }

    try
    {
        var cookie = WebView.Cookies[Settings.CookiesSettingsKey];

        Settings.CookiesSettings = cookie.Value;
    }
    catch (Exception)
    {
    }

    Loader.IsVisible = Loader.IsRunning = false;
}

In a native iOS app I would have started investigating layout and things like setNeedsDisplay, but I haven't yet found out how to do that with Xamarin.

Thanks for helping out!