DataTables - Row grouping with Buttons

Clicking on any button to view problem with datatable

HTML

<link rel="stylesheet" href="https://cdn.datatables.net/1.10.18/css/dataTables.bootstrap4.min.css">
<script src="https://cdn.datatables.net/1.10.18/js/jquery.dataTables.min.js"></script>
<script src="https://cdn.datatables.net/1.10.18/js/dataTables.bootstrap4.min.js"></script>
<link rel="stylesheet" href="https://cdn.datatables.net/buttons/1.5.6/css/buttons.bootstrap4.min.css">
<script src="https://cdn.datatables.net/buttons/1.5.6/js/dataTables.buttons.min.js"></script>
<script src="https://cdn.datatables.net/buttons/1.5.6/js/buttons.bootstrap4.min.js"></script>
<script src="https://cdn.datatables.net/buttons/1.5.6/js/buttons.colVis.min.js"></script>
<link rel="stylesheet" href="https://cdn.datatables.net/rowgroup/1.1.0/css/rowGroup.bootstrap4.min.css">
<script src="https://cdn.datatables.net/rowgroup/1.1.0/js/dataTables.rowGroup.min.js"></script>
<link rel="stylesheet" href="https://cdn.datatables.net/fixedheader/3.1.4/css/fixedHeader.bootstrap4.min.css">
<script src="https://cdn.datatables.net/fixedheader/3.1.4/js/dataTables.fixedHeader.min.js"></script>
<table class="table table-sm dataTable" id="myDataTable" role="grid">
  <thead>
    <tr role="row">
      <th rowspan="2" colspan="1">Hidden</th>
      <th rowspan="2" colspan="1">Area</th>
      <th rowspan="1" colspan="14">Initial Grade Level</th>
      <th rowspan="1" colspan="14">Highest Grade Level</th>
      <th rowspan="1" colspan="2">Average Test Score</th>
      <th rowspan="2" colspan="1">One Grade Level Gain</th>
      <th rowspan="1" colspan="2">Quick Gain</th>
    </tr>
    <tr role="row">
      <th>0.0-0.9</th>
      <th>1.0-1.9</th>
      <th>2.0-2.9</th>
      <th>3.0-3.9</th>
      <th>4.0-4.9</th>
      <th>5.0-5.9</th>
      <th>6.0-6.9</th>
      <th>7.0-7.9</th>
      <th>8.0-8.9</th>
      <th>9.0-9.9</th>
      <th>10.0-10.9</th>
      <th>11.0-11.9</th>
      <th>12.0-12.9</th>
      <th>Unknown</th>

      <th>0.0-0.9</th>
      <th>1.0-1.9</th>
      <th>2.0-2.9</th>
     ...

TypeScript

let readingTableData: Array < any > =...