Bootstrap Modal Focus not working

Try this (autofocus added to your link):

<input name="referencia" id="referencia" type="text" class="form-control text-uppercase" placeholder="Descripci&oacute;n" autofocus>

or try this:

$('#myModal').on('shown.bs.modal', function () {
    $('#myInput').focus();
})

or this:

// Every time a modal is shown, if it has an autofocus element, focus on it.
$('.modal').on('shown.bs.modal', function() {
  $(this).find('[autofocus]').focus();
});