Been kind of distracted lately, just noticed that the other meta box fields were blank within the editor. I'm guessing the data isn't there until the repeater content is display on the frontend.
I added
<?php
if (rwmb_meta( 'music', '', $postal )) : ;
$postal = get_the_id();
$values = rwmb_meta( 'music', '', $postal ) ;
echo 'Music: ';
foreach ( $values as $value ) {
echo $value;
echo '<br />';
}
endif;
?>
Error is gone and everything works ok on the frontend.