toolbar items not dsiplay in dropdownlist after set order as secondary

hi
we develop a xamarin forms 4.x app using shell.The issue in is toolbar items not show in dropdownlist after set order as secondary. my code as below:

<ContentPage.ToolbarItems> <ToolbarItem Text="Reload" Priority="0" Clicked="ToolbarItem_Clicked_1" Order="Primary" /> <ToolbarItem Text="Sort" Priority="0" Clicked="ToolbarItem_Clicked" Order="Secondary" /> <ToolbarItem Text="Select" Priority="0" Clicked="ToolbarItem_Clicked_2" Order="Secondary" /> <ToolbarItem Text="Update Selected" Priority="0" Clicked="ToolbarItem_Clicked_3" Order="Secondary" /> </ContentPage.ToolbarItems>