No images showing when I try to set caching on for images in a ListView

Newbie to Xamarin Forms and I'm trying to add caching to images in a ListView to see if it improves performance on the scroll. When I add this code:

              <abstractions:CircleImage HeightRequest="80" WidthRequest="80" BorderColor="Black" BorderThickness="2" >
                <abstractions:CircleImage.Source>
                  <UriImageSource Uri="{Binding ProductImageUrl}" CacheValidity="12" CachingEnabled="True"/>
                </abstractions:CircleImage.Source>
              </abstractions:CircleImage>

No images show up, but when I revert back to setting the image source like this:

     <abstractions:CircleImage HeightRequest="80" WidthRequest="80" BorderColor="Black" BorderThickness="2" Source="{Binding ProductImageUrl}"/ >

The images appear. Is there something that I'm missing for trying to cache the images?

Thanks