Doesn't display list when I set this to the field multiple

{% for post in query.posts %}
	<a href="{{ post.post_related.url }}">{{ post.post_related.title }}</a>
    {{ post.post_related.date | date( 'F j, Y' ) }}
	{{ mb.get_the_term_list( post.post_related.ID, 'category', '', ', ' ) }}
    {{ post.post_related.post_comments() }}
	<img src="{{ post.post_related.thumbnail.full.url }}" width="{{ post.post_related.thumbnail.full.width }}" height="{{ post.post_related.thumbnail.full.height }}" alt="{{ post.post_related.thumbnail.full.alt }}">
{% endfor %}

<?php
add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );

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

    $meta_boxes[] = [
        'title'  => __( 'Related Post', 'your-text-domain' ),
        'id'     => 'related-post',
        'fields' => [
            [
                'name'       => __( 'Post', 'your-text-domain' ),
                'id'         => $prefix . 'post_related',
                'type'       => 'post',
                'post_type'  => ['post'],
                'field_type' => 'select_advanced',
                'multiple'   => true,
            ],
        ],
    ];

    return $meta_boxes;
}