Facebook customer chat plugin disappering when refresh page

Question

I added this code for facebook customer chat plugin to my website www.sifucode.com

<!-- Load Facebook SDK for JavaScript -->
  <div id="fb-root"></div>
  <script>
    window.fbAsyncInit = function() {
      FB.init({
        xfbml            : true,
        version          : 'v8.0'
      });
    };

    (function(d, s, id) {
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id)) return;
    js = d.createElement(s); js.id = id;
    js.src = 'https://connect.facebook.net/en_US/sdk/xfbml.customerchat.js';
     fjs.parentNode.insertBefore(js, fjs);
  }(document, 'script', 'facebook-jssdk'));</script>

  <!-- Your Chat Plugin code -->
  <div class="fb-customerchat"
    attribution=setup_tool
    page_id="<pageid>">
  </div> 

the chat box is appearing when my website opens first. but then if you refresh the page the chatbox is disappering. I tried chrome and safari. I got same results. what is problem ?