I have created a usercontrol which uses

        <UserControl .......           
         MouseMove="UserControl_MouseMove" 
         MouseLeftButtonUp="UserControl_MouseLeftButtonUp">

and I have created a singleton class which only updates once the parameter changes:

public class PopUpMovement
{
    private PopUpMovement() { }

    private static PopUpMovement _instance;
    private static readonly object _instanceLock = new object();

    public static PopUpMovement Instance()
    {
        if (_instance == null)
        {
            lock (_instanceLock)
            {
                if (_instance == null)
                {
                    _instance = new PopUpMovement();
                }
            }
        }

        return _instance;
    }

    public bool draggingPopup { get; set; }
    public bool CustomTablePopupClicked { get; set; }
}

My code in the code behind of usercontrol:

    private Point startPoint;
    private double initialHorizontalOffset;
    private double initialVerticalOffset;
    private Point initialMousePosition;
    private Point startDragPoint;
    //private bool CustomTablePopupClicked;
    private void UserControl_MouseMove(object sender, MouseEventArgs e)
    {

        if (PopUpMovement.Instance().draggingPopup)
        {
            else if (PopUpMovement.Instance().CustomTablePopupClicked)
            {
                Point currentMousePosition = e.GetPosition(this); // Get the mouse position relative to the UserControl
                double offsetX = currentMousePosition.X - initialMousePosition.X;
                double offsetY = currentMousePosition.Y - initialMousePosition.Y;

                CustomTablePopup.HorizontalOffset += offsetX;
                CustomTablePopup.VerticalOffset += offsetY;

                initialMousePosition = currentMousePosition; // Update initial position
            }
        }
    }

    private void UserControl_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        if(PopUpMovement.Instance().draggingPopup == true)
        {
            PopUpMovement.Instance().draggingPopup = false;
            PopUpMovement.Instance().CustomTablePopupClicked = false;
            Mouse.Capture(null);
        }
    }


    private void CustomTablePopup_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        // Store the mouse position
        //draggingPopup = true;
        //PopUpMovement popUpMovement = PopUpMovement.Instance();
        //popUpMovement.draggingPopup = true;
        PopUpMovement.Instance().draggingPopup = true;
        initialMousePosition = e.GetPosition(this); // Get the mouse position relative to the Window
        Mouse.Capture(this); // Capture mouse at the UserControl level
    }

It works fine if the user moves the popup window for the first time, however, if the user wants to move it again nothing happens it stays fixed. So, How can I fix the code so that the user can move the popup box anywhere the user wants?