TabbedPage issue in Android position

Ciato,
i am using the xanimals app as an example to implement shells in my new app. I inserted a TabbedPage. All right until I move the tabs down with the following instructions:

xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
            android:TabbedPage.ToolbarPlacement="Bottom"
              android:TabbedPage.BarItemColor="Gray"
             android:TabbedPage.BarSelectedItemColor="White"

tab layout has some problems.

is it to you?
at the moment I have to abandon this road ...
(all nuget packages are updated)