Session variables only work in the development environment (JSP)

I am developing a web page with JavaServer Pages and I am facing the following problem: The page works correctly where I am developing (I use NETBEANS for it). When giving " Run Project `" the page receives the session variables very well.

When I give " Clean and build " to generate the file .WARto upload it to my hosting, and I execute the page from the domain (from the hosting), at times I lose the value contained in the session variable, and as a result of this, as a consequence they leave errors (the classic " Java Null Pointer Exception").

How am I manipulating the session variables? Ok, here are some snippets of code:

This right here is a servlet to login. I am saving two data, the user name and the user type. In addition to that, I establish a lifetime (1 hour):

Login log = new Login();   

    log.setEmail(request.getParameter("username"));
    log.setPassword(request.getParameter("password"));

    try {
        if (log.iniciarSesion()) {
            HttpSession session = request.getSession(false); <---- Llamo la sesion
            session.setAttribute("username", log.getEmail()); <---- guardo usuario
            session.setAttribute("tipo", log.getTipoUser().charAt(0)); <---- guardo tipo
            MessageController.setError(false);
            session.setMaxInactiveInterval(3600); <---- ajusto tiempo de vida (3600 segundos)
            switch (log.getTipoUser().charAt(0)) {
                case 'T':
                    response.sendRedirect("ListaObrasServlet?page=1");
                    break;
                case 'S':
                    response.sendRedirect("ListaTitularServlet?page=1");
                    break;
                default:
                    response.sendRedirect("ObrasServlet?page=1");
                    break;
            }
        } else {
            MessageController.setError(true);
            response.sendRedirect("index.jsp");
        }
    } catch (SQLException ex) {
        Logger.getLogger(LoginServlet.class.getName()).log(Level.SEVERE, null, ex);
    }

Now an example of how I retrieve the values:

<nav class="gtco-nav" role="navigation">
                <div class="gtco-container">

                    <div class="row">
                        <div class="col-sm-4 col-xs-12">
                            <div id="gtco-logo"><a href="index.jsp">VUDA </a></div>
                        </div>
                        <div class="col-xs-8 text-right menu-1">
                            <ul> 
                                <% if(session.getAttribute("tipo").toString().contains("U")){ %>
                                    ETC ETC ETC ETC
                                     <% }else if(session.getAttribute("tipo").toString().contains("T")){%>
                                    ETC ETC ETC ETC
                                <% }else if(session.getAttribute("tipo").toString().contains("S")){ %>
                                    ETC ETC ETC ETC
                                <%}%>
                                (mas y mas html)
                                <% if(session.getAttribute("tipo").toString().contains("U") ){%>
                                    ETC ETC ETC ETC
                                <% } %>
                                <li><a href="#">Contactenos</a></li>
                                  <li  class="btn-cta" <% if(session.getAttribute("username")!=null ) out.print("style='display:none;'");%>><a id="btn2" data-toggle="modal" data-target="#loginModal"><span>Usuario</span></a></li>
                                <li  class="btn-cta" <% if(session.getAttribute("username")!=null ) out.print("style='display:inline;'");else out.print("style='display:none;'");%>><a href="logoutServlet"><span>Cerrar Sesion</span></a></li>
                            </ul>
                        </div>
                    </div>

                </div>
            </nav>

Well, as I was saying, I repeat the problem: everything works fine when I run from netbeans , but when I upload the page to the hosting, I lose the value contained in the session when I change the page . There are moments when everything works fine, but out of nowhere that happens.

Note: In the XML file I also have the life time of the sessions with this:

<session-config>
    <session-timeout>
        60
    </session-timeout>
</session-config>

What could it be?

UPDATE: I discovered that the session actually dies as soon as you change the page in the hosting, and I don't understand why (The server is an Ubuntu Server). What is Netbeans supposed to do to keep them alive?

I'm pretty sure it's a configuration issue. On the server, in order to keep the sessions alive on each page, I have to use encodeURL... but this is too annoying for me. How do I make the GlassFish server keep the session alive? What I use in my Stack Web is:

• Operating System: Ubuntu Server 18.04 LTS

• Web Server: GlassFish Server 4.1.1

• Database: MySQL

• Programming language: Java Server Pages