Hi Ryan,
I've just done a quick test and it works for me. Here is the code I'm using to register a meta box and filter the label:
add_filter( 'rwmb_meta_boxes', function( $meta_boxes ) {
$meta_boxes[] = [
'title' => 'Cloneable Post Field',
'fields' => [
[
'id' => 'p',
'title' => 'Post',
'type' => 'Post',
'clone' => true,
],
],
];
return $meta_boxes;
} );
add_filter( 'rwmb_p_choice_label', function ( $label, $field, $post ) {
return "$post->post_type: $post->post_title";
}, 10, 3 );
And here is the screenshot:
https://prnt.sc/opcstu