Setting value works on Android but not on UWP

Hi
I'm trying to set the value of Slider (XAML), using
mySlider.value = 10;

now it works on Android like a fox
but it does not works on UWP

for some reason it does not even work in the XAML:
Slider x:Name="mySlider" Maximum="31" Minimum="17" Value="25"/

Any idea how to set the slider value on UWP?