Why does my eventDrop only working for weekly and daily view? For the monthly view, eventDrop works when under inspect only

Question

I am truly confused with what is happening but here is my code that I believe, is related to the problem. As mentioned, ONLY the eventDrop is not working for the monthly view. While in weekly and daily view, eventDrop works. And if I open the web under inspect, the eventDrop works fine. Would love to know the solutions! Thanks in advance.

<meta charset="utf-8">
    <title>Calendar</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" integrity="sha384-wvfXpqpZZVQGK6TAh5PVlGOfQNHSoD2xbE+QkPxCAFlNEevoEH3Sl0sibVcOQVnN" crossorigin="anonymous">
    <link rel="stylesheet" type="text/css" href="testing.css">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/3.4.0/fullcalendar.css" />
  <!-- <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-alpha.6/css/bootstrap.css" /> -->
  <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/3.4.0/fullcalendar.min.js"></script>
  
  <script>
      function toggleMenu(){
            let toggle=document.querySelector('.toggle');
            let navigation=document.querySelector('.navigation');
            let main=document.querySelector('.main');
            toggle.classList.toggle('active');
            navigation.classList.toggle('active');
            main.classList.toggle('active');
        }
  $(document).ready(function() {
   var calendar = $('#calendar').fullCalendar({
    displayEventTime: false,
    editable:true,
    header:{
     left:'prev,next today',
     center:'title',
     right:'month,agendaWeek,agendaDay'
    },
    events: 'load.php',
    selectable:true,
    selectHelper:true,
    select: function(start, end, allDay)
    {
     var title = prompt("Enter Event Title");
     if(title)
     {
      var start = $.fullCalendar.formatDate(start, "Y-MM-DD HH:mm:ss");
      var end = $.fullCalendar.formatDate(end, "Y-MM-DD HH:mm:ss");
      $.ajax({
       url:"insert.php",
       type:"POST",
       data:{title:title, start:start, end:end},
       success:function()
       {
        calendar.fullCalendar('refetchEvents');
        alert(title+" added successfully.");
       }
      })
     }
    },
    editable:true,
    eventResize:function(event)
    {
     var start = $.fullCalendar.formatDate(event.start, "Y-MM-DD HH:mm:ss");
     var end = $.fullCalendar.formatDate(event.end, "Y-MM-DD HH:mm:ss");
     var title = event.title;
     var id = event.id;
     $.ajax({
      url:"update.php",
      type:"POST",
      data:{title:title, start:start, end:end, id:id},
      success:function(){
       calendar.fullCalendar('refetchEvents');
       alert(title+" updated.");
      }
     })
    },

    eventDrop:function(event)
    {
     var start = $.fullCalendar.formatDate(event.start, "Y-MM-DD HH:mm:ss");
     var end = $.fullCalendar.formatDate(event.end, "Y-MM-DD HH:mm:ss");
     var title = event.title;
     var id = event.id;
     $.ajax({
      url:"update.php",
      type:"POST",
      data:{title:title, start:start, end:end, id:id},
      success:function()
      {
       calendar.fullCalendar('refetchEvents');
       alert(title+" updated.");
      }
     });
    },

    eventClick:function(event)
    {
     if(alert("event name : "+event.title+"\nstart date : "+event.start+"\nend date : "+event.end))
     {
      var id = event.id;
      $.ajax({
       url:"display.php",
       type:"POST",
       data:{id:id},

       success:function()
       {
        calendar.fullCalendar('refetchEvents');
        //alert("event name : "+event.title+"\nstart date : "+event.start+"\nend date : "+event.end);
        alert("Event Removed");
       }
      })
      }
    },

   });
  });