Footers require some extra code modules.
You’ll need to add these files to your manifest:
fixedHeader.bootstrap.min.css
dataTables.fixedHeader.min.js
You’ll need to add this to systemheaders:
<link rel="stylesheet" href="fixedHeader.bootstrap.min.css"/>
<script src="dataTables.fixedHeader.min.js"></script>
You can get the files here:
https://datatables.net/download/index