Odering icon missing

I have implemented datatables in wordpress. The Table are shown, but the icon to chance the ordering are missing. I have no idea why.
The JS Script:

jQuery( document ).ready( function() {
  var ajaxurl = '/wp-content/plugins/finswim-cup-tools/admin/fsct-server-processing.php?cy=' + php_vars.cy;

  jQuery( '#fsct_admin_rank_table' ).DataTable( {
    dom: "<'row'<'col-sm-4'l><'col-sm-4 DT_Buttons_Style'B><'col-sm-4'f>>rt<'row'<'col-sm-6'i><'col-sm-6'p>>",
        ajax: {
            url: ajaxurl,
            type: 'POST'
    },
    columnDefs: [
      { targets: 0, orderable: true },
      { targets: 1, visible: true, searchable: true, orderable: true },
      { targets: 2, visible: true, searchable: true, orderable: true }
      { targets: '_all', searchable: false, orderable: false }
    ],
    order: [ [ 0, 'asc' ] ],
    processing: true,
        serverSide: true,
        columns: [
            { data: 'athlete.lastname', width: '25%' },
            { data: 'athlete.firstname', width: '20%' },
            { data: 'agegroup', width: '4%', className: 'text-center' },
      { data: 'agrd1', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd2', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd3', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd4', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd5', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
            { data: 'agtotal', width: '5%', className: 'text-center' },
      { data: 'agrd1', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd2', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd3', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd4', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
      { data: 'agrd5', render: function( data, type, row ){
        if(type === 'display'){
          return ( data == 0 ) ? '' : data;
        } }, className: 'text-center'
      },
            { data: 'agtotal', width: '5%', className: 'text-center' }
    ],
    select: true,
    ordering: false,
    autoWidth: false,
    buttons: [
      {
                extend: "pdfHtml5",
                text: '<i class="fa fa-file-pdf-o text-red"></i>',
                titleAttr: 'Export to PDF',
      }
    ]
  } );
} );

There is no possible way to send a ordering. The $_POST for column 0 looks like this:

   columns[0][data]: athlete.lastname
   columns[0][name]:
   columns[0][orderable]: false
   columns[0][search][regex]: false
   columns[0][search][value]:
   columns[0][searchable]: true

Anyone a idea where my fault is?