When using ScrollY the header becomes locked and will sometimes mis-align. The main issue is when scrolling horizontally the header does not move and if there are headers off screen you never see them.
HTML:
(example table from https://datatables.net/examples/basic_init/zero_configuration.html)
CSS:
td { white-space: nowrap; }
th { white-space: nowrap; }
js:
$("#example").DataTable({
dom: 'Bfrtip',
"scrollY": "35vh",
"scrollCollapse": true,
"paging": false
});
Example showing the issue:
http://jsfiddle.net/Cyberjetx/hgvtqxux/34/