Random Image Placement

So I have a Canvas and a set of 18 Images in it and I want to random the Images inside it

    foreach (var myImg in GameCanvas.Children.OfType<Image>())
{
    GetTop.Add(Canvas.GetTop(myImg));
    GetLeft.Add(Canvas.GetLeft(myImg));
    myImg.IsTapEnabled = false;
}

I have this part to add the Top and Left of each image in a separate list BUT when I try this

foreach (var myImg in GameCanvas.Children.OfType<Image>())
    {           
        int ran = rand.Next(GetTop.Count);
        double Top = GetTop[ran];
        double Left = GetLeft[ran];
        Canvas.SetTop(myImg, Top);
        Canvas.SetLeft(myImg, Left);
        GetTop.Remove(Top);
        GetLeft.Remove(Left);
    }

the Images change places but some of them disappear completely and the rest change places as intended. I don't get why that happens. Any Idea?