Custom ordering of the Enfold Woocommerce slider

Hi all,
I need to order posts in the Woocommerce Slider integrated in Enfold by a custom meta, which happens a date.
I am not sure I understand the filter capability, but I tried the short plugin below, with no effect. The custom ordering is not appearing in the dropdown menu. I am overiding the priority of Enfold ordering by a priority, but I would be more than happy to use more elegant solution if possible, and this does not work anyway…

<?php

// Add custom sorting option to Enfold's sorting dropdown
add_filter( 'avf_wc_product_order_dropdown_frontend', 'add_custom_sorting_option' );

function add_custom_sorting_option( $product_order ) {
    $product_order['course_date'] = __( 'Sort by course date', 'woocommerce-course-date-sorting' );
    return $product_order;
}

// Modify the ordering arguments after Enfold's modifications
add_filter( 'woocommerce_get_catalog_ordering_args', 'custom_catalog_ordering_args', 30 );

function custom_catalog_ordering_args( $args ) {
    if ( isset( $_GET['product_order'] ) && 'course_date' === $_GET['product_order'] ) {
        $order = isset( $_GET['product_sort'] ) ? strtoupper( $_GET['product_sort'] ) : 'ASC';
        $args['orderby'] = 'meta_value';
        $args['order'] = $order;
        $args['meta_key'] = '_course_date';
        $args['meta_type'] = 'DATE';
    }
    return $args;
}

// Modify the product query to include only products with '_course_date' meta key
add_action( 'woocommerce_product_query', 'custom_woocommerce_product_query' );

function custom_woocommerce_product_query( $query ) {
    if ( ! is_admin() && $query->is_main_query() && is_shop() ) {
        if ( isset( $_GET['product_order'] ) && 'course_date' === $_GET['product_order'] ) {
            $meta_query = $query->get( 'meta_query' );
            if ( ! is_array( $meta_query ) ) {
                $meta_query = array();
            }
            $meta_query[] = array(
                'key'     => '_course_date',
                'compare' => 'EXISTS',
            );
            $query->set( 'meta_query', $meta_query );
        }
    }
}

Can you please guide me on how to tackle this properly? Thanks, Jakub