IsVisible inside Control inside StackLayout inside ScrollView not work?

Hello!
I use this scheme of form like this:

Content= new ScrollView { HorizontalOptions=LayoutOptions.Fill, VerticalOptions=LayoutOptions.Fill, Content= new StackLayout { HorizontalOptions=LayoutOptions.FillAndExpand, VerticalOptions=LayoutOptions.FillAndExpand, Childrent= { Control1 { IsVisible=false}, Control2 { IsVisible=false}, Control3 { IsVisible=false}, Control4 { IsVisible=false}, Control5 { IsVisible=false}, Control6 { IsVisible=false}, Control7 { IsVisible=false}, } } };

When need, i change "IsVisible" property of controls from "false" to "true".
And some time (not every time!) some controls not appear! I see empty space in stack layout, but not controls. It seems like this:

"
label1
label2
label3

label5

label7
"

Some time not appear any of control, some time - appear all of them.
Does anyone know why this is happening?