To reproduce:

private void RadButton1_Click(object sender, EventArgs e)
{
    Telerik.WinControls.UI.RadDesktopAlert _Alert = new Telerik.WinControls.UI.RadDesktopAlert();
    _Alert.CaptionText = "TEST ALERT";
    _Alert.ContentText = "This is my test content";
    _Alert.AutoSize = true;
    //RadDirection.Up bug when the screen is scaled (for example set creen scale at 150% => alert is cut, part of the window is not visible and the direction is still down)
    //Whereas RadDirection.Down seems to work fine
    _Alert.PopupAnimationDirection = Telerik.WinControls.UI.RadDirection.Down;
    _Alert.Show();
}