Xamarin Forms ScrollView displays blank screen - xaml

Question

The following XAML shows my page just fine, until I added the ScrollView , now it just displays a blank screen.
Can anyone spot anything obvious with this? I suspect it my be because I'm setting the height of the grid within the ScrollView but I'm not sure
<ContentPage.Content>
<ScrollView>
<Grid BackgroundColor="#ede8db" x:Name="articleGrid" >
<Grid.RowDefinitions>
<RowDefinition Height="47.5*" />
<RowDefinition Height="5*" />
<RowDefinition Height="47.5*" />
</Grid.RowDefinitions>
<ratio:ContentRatioContainer Grid.Row="0" x:Name="imgContainer">
<Image Aspect="AspectFill" Source="KevingroveCarouselImg.png" AbsoluteLayout.LayoutBounds="1,1,1,1" AbsoluteLayout.LayoutFlags="All" x:Name="bigImg"
HeightRequest="{artina:OnOrientationDouble PortraitPhone=880, LandscapePhone=125, PortraitTablet=600, LandscapeTablet=400 }" Grid.Row="0"/>
</ratio:ContentRatioContainer>
<artina:Button Margin="10,10,10,10" x:Name="ImgZoom" Clicked="EnlargeImage" HorizontalOptions="End" VerticalOptions="Start" Image="IncreaseImageIcon.png" BackgroundColor="Transparent" HeightRequest="30" WidthRequest="30"/>
<StackLayout Grid.Row="1" Orientation="Horizontal" BackgroundColor="#ede8db" Margin="0" Padding="30,0,30,0" x:Name="iconStack" HorizontalOptions="FillAndExpand" >
<Label HorizontalTextAlignment="Center" Text="{x:Static ratio:FontAwesome.WIFI}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="{artina:OnOrientationDouble PortraitPhone=25, LandscapePhone=18, PortraitTablet=30, LandscapeTablet=20 }" />
<Label HorizontalTextAlignment="Center" Text="{x:Static ratio:FontAwesome.CAMERA}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="{artina:OnOrientationDouble PortraitPhone=25, LandscapePhone=18, PortraitTablet=30, LandscapeTablet=20 }" />
<Label HorizontalTextAlignment="Center" Text="{x:Static ratio:FontAwesome.MAP}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="{artina:OnOrientationDouble PortraitPhone=25, LandscapePhone=18, PortraitTablet=30, LandscapeTablet=20 }" />
<Label x:Name="expand" HorizontalTextAlignment="Center" HorizontalOptions="EndAndExpand" Text="{x:Static ratio:FontAwesome.ARROW_DOWN}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="{artina:OnOrientationDouble PortraitPhone=25, LandscapePhone=18, PortraitTablet=30, LandscapeTablet=20 }" />
</StackLayout>
<StackLayout Grid.Row="2" x:Name="articleInfo" Padding="30,0,30,0" >
<StackLayout x:Name="TopLayout" Opacity="0.0">
<StackLayout Orientation="Horizontal">
<Label HorizontalTextAlignment="Center" Text="{x:Static ratio:FontAwesome.MAP_MARKER}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="30" />
<Label Text="Address" VerticalOptions="Center" HorizontalOptions="StartAndExpand" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Label HorizontalTextAlignment="Center" Text="{x:Static ratio:FontAwesome.CLOCK_O}" Style="{StaticResource FontIcon}" TextColor="Black" FontSize="30" />
<Label Text="Openening Times" VerticalOptions="Center" HorizontalOptions="StartAndExpand" />
</StackLayout>
<StackLayout x:Name="EmptySpaceStack" HeightRequest="80" />
<StackLayout x:Name="txt" >
<Label x:Name="header" Text="HEADER" Style="{ StaticResource HeaderStyle }" />
<Label x:Name="description" Text="TEST" FontSize="Large" />
<Label x:Name="articleTxt" Text="BLAH..." FontSize="Medium"/>
</StackLayout>
</StackLayout>
</StackLayout>
</Grid>
</ScrollView>
</ContentPage.Content>
UPDATE
looks like it's the ContentRationContainer that causes the problem, just to figure out why...
public class ContentRatioContainer : ContentView
{
public double ratio;
protected override SizeRequest OnMeasure(double widthConstraint, double heightConstraint)
{
var width = Application.Current.MainPage.Width;
var height = Application.Current.MainPage.Height;
if (Device.Idiom == TargetIdiom.Phone)
{
ratio = Convert.ToDouble(Resx.AppResources.ImageRatioContentPhone);
}
if (Device.Idiom == TargetIdiom.Tablet)
{
if (width > height)
{
ratio = Convert.ToDouble(Resx.AppResources.ImageRatioContentTabL);
}
else
{
ratio = Convert.ToDouble(Resx.AppResources.ImageRatioContentTabP);
}
}
return new SizeRequest(new Size(widthConstraint, widthConstraint * ratio));
}
public static BindableProperty ContentRatioProperty = BindableProperty.Create(nameof(ContentRatio), typeof(double), typeof(ContentRatioContainer), (double)1);
public double ContentRatio
{
get { return (double)this.GetValue(ContentRatioProperty); }
set { this.SetValue(ContentRatioProperty, value); }
}
}