cmb2/js/cmb2.jsand edit line 499, changing
$table.find('.cmb-repeatable-grouping').last();to '$table.find('.cmb-repeatable-grouping').first();' and edit line 508. changing
$oldRow.after( $newRow );into
$oldRow.before( $newRow );it will do what you want. However you would probably want more to make sure the page scrolls to the new row. Also this will not affect how the rows load from the server.
.on('change')so when the page loads all fields are hidden until the select box is changed. Also when I add a new repeater block the .on(change) has no effect.