Configure (Set) Session Idle Timeout in IIS

Hello, Please I need help on a very problem I encountered in my application.

After login I notice that I get logged out quickly, even though I set my sessionState timeout to "80".

This never happened before today. I logged in and was redirected to my dashboard, then from there I moved to next page and when I tried to return to the dashboard, I was logged out and redirected to login page.

Please is there anything I did wrong in this my web.config file?

Is there something that should not be there?

Also, here is the page load event of my pages:

protected void Page_Load(object sender, EventArgs e) 
{ 
    if (this.Page.User.Identity.IsAuthenticated && Session["user"] != null) 
    { 
        named.Visible = true; Units.Visible = true;
        unitlbl.Visible = true;
        createby.Visible = false;
        id.Visible = true;
        Showdata();
        Showdata1();
    } 
    else 
    { 
        // Response.Redirect("https://quirver.com/login"); 
    } 
    Response.Cache.SetCacheability(HttpCacheability.NoCache); 
    Response.Cache.SetExpires(DateTime.Now.AddSeconds(-1)); 
    Response.Cache.SetNoStore(); 
    Response.AppendHeader("Pragma", "no-cache"); 
}