Pre-selecting terms in an taxonomy-advanced field

I have a taxonomy_advanced meta field in a user meta box. The taxonomy is a non-hierarchical custom user taxonomy.

What I want to do is pre-select the choices/terms in the taxonomy field based on the terms currently assigned to the user that is being edited in WP admin. I'm using the rwmb_field_meta filter and the function below to filter the meta value when the field loads.

$meta contains a comma-separated list of assigned term IDs as expected. But only the first term in the taxonomy field is pre-selected when the user edit admin screen is loaded.

What do I have to do differently to pre-select ALL the assigned terms in the taxonomy meta field?

public function populate_user_tags_meta( $meta, $field, $saved ) {
    if( is_admin() ) {
        // Get the user ID for the currently viewed user profile.
        if( defined('IS_PROFILE_PAGE') && IS_PROFILE_PAGE ) {
            // If is current user's profile (profile.php)
            $user_id = get_current_user_id();
        } elseif( !empty($_GET['user_id']) && is_numeric($_GET['user_id']) ) {
            // If is another user's profile page
            $user_id = $_GET['user_id'];
        } else {
            // Otherwise something is wrong.
            die( 'No user ID defined.' );
        }
        // Get the user tags currently assigned to this user.
        $current_users_tags = wp_get_object_terms( $user_id, 'wv_user_tag', array('fields' => 'ids') );
        // Populate meta value with comma-separated string of currently assigned user tag IDs.
        if( !empty($current_users_tags) && !is_wp_error($current_users_tags) ) {
            $meta = implode( ',', array_filter( array_unique( (array) $current_users_tags ) ) );
        } else {
            $meta = '';
        }
    }
    return $meta;
}