Shortcode will not show custom field group

Hi,

I have a strange issue that has been driving me crazy. I have a published field group that will not display on the front end via shortcode.

I have several other shortcodes that are almost identical (different custom field groups) and displaying content on the front end in Beaver Themer, but no matter what I do this one only ever returns an empty() result for the custom fields.

Can anyone give me any suggestions as to why I can retrieve and display these custom fields on the front end?

Here's the code from the custom fields settings:

add_filter( 'rwmb_meta_boxes', 'your_prefix_register_meta_boxes' );

function your_prefix_register_meta_boxes( $meta_boxes ) {
    $prefix = '';

    $meta_boxes[] = array (
        'title' => esc_html__( 'Composition', 'text-domain' ),
        'id' => 'composition',
        'post_types' => array(
            0 => 'sock',
        ),
        'context' => 'normal',
        'priority' => 'low',
        'fields' => array(
            array (
                'id' => $prefix . 'percent_combed_cotton',
                'type' => 'number',
                'name' => esc_html__( 'Combed Cotton', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_cotton',
                'type' => 'number',
                'name' => esc_html__( 'Cotton', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_nylon',
                'type' => 'number',
                'name' => esc_html__( 'Nylon', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_elastane',
                'type' => 'number',
                'name' => esc_html__( 'Elastane', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_spandex',
                'type' => 'number',
                'name' => esc_html__( 'Spandex', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_wool',
                'type' => 'number',
                'name' => esc_html__( 'Wool', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_merino',
                'type' => 'number',
                'name' => esc_html__( 'Merino Wool', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_acrylic',
                'type' => 'number',
                'name' => esc_html__( 'Acrylic', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
            array (
                'id' => $prefix . 'percent_elastic',
                'type' => 'number',
                'name' => esc_html__( 'Elastic', 'text-domain' ),
                'max' => 100,
                'step' => 1,
                'columns' => 3,
            ),
        ),
    );

    return $meta_boxes;
}

Here is the shortcode:

/**
 * @return false|string
 *
 * Shortcode to display compositon
 */
function sock_composition_func()
{
    $sockcomp = rwmb_meta('composition');

    ob_start();

    if ( empty( $sockcomp ) ) {
        return 'no sock composition found';
    }

    print_r($sockcomp);  // my output code will go here but it never displays because $sockcomp always returns empty()

    return ob_get_clean();
}
add_shortcode('sock_composition', 'sock_composition_func');