Vaadin 8 Session created twice

Dear,
Right now I am tracking some of the vaadin session issues for our application, and did find vaadin create session twice when we connect to the server. From my understanding, only one session should be created for each user.
The code and logs are as below.

    @WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false)
    public static class MyUIServlet extends VaadinServlet implements SessionInitListener, SessionDestroyListener
    {
        @Override
        protected void servletInitialized() throws ServletException
        {
            super.servletInitialized();
            getService().addSessionInitListener( this );
            getService().addSessionDestroyListener( this );
        }
        @Override
        public void sessionDestroy( SessionDestroyEvent event )
        {
            logger.error( "**Session destroyed id = " + event.getSession().getSession().getId() );
        }
    
        @Override
        public void sessionInit( SessionInitEvent event ) throws ServiceException
        {
            logger.error( "**Session created id = " + event.getSession().getSession().getId() );
        }
    }
Dec 18, 2019 4:58:46 PM com.MyUI$MyUIServlet sessionInit
SEVERE: **Session created id = 4A7C3FE9C37F5EE224B9E3968D4B2D70
Dec 18, 2019 4:58:47 PM com.MyUI$MyUIServlet sessionInit
SEVERE: **Session created id = C813F3360209D4F22AB2E2ECFCED5DCA