Sometimes Xamarin can be full of bugs, scroll views and z index are one of them.
With Xamarin Forms, the Z Index is controlled by the order that the views appear in the Xaml, this is the easiest way to bring a view to front, just define it first.
ScrollView's are a little buggy, you might find that the content within a ScrollView will overlap the content around it instead of clipping at the border of the ScrollView. This isn't a simple matter of reordering the Xaml, this is a bug and the way around it for most people is to add the following to your ScrollView.
By Luke Alderton at 17 Jul 2016, 08:09 AM