Actually, the support for my theme told me that this is a Woocommerce problem, no the theme.
I did find the code above in wp-content/plugins/woocommerce/includes/wc-template-functions.php
function woocommerce_subcategory_thumbnail( $category ) {
$small_thumbnail_size = apply_filters( 'subcategory_archive_thumbnail_size', 'shop_catalog' );
$dimensions = wc_get_image_size( $small_thumbnail_size );
$thumbnail_id = get_woocommerce_term_meta( $category->term_id, 'thumbnail_id', true );
if ( $thumbnail_id ) {
$image = wp_get_attachment_image_src( $thumbnail_id, $small_thumbnail_size );
$image = $image[0];
$image_srcset = function_exists( 'wp_get_attachment_image_srcset' ) ? wp_get_attachment_image_srcset( $thumbnail_id, $small_thumbnail_size ) : false;
$image_sizes = function_exists( 'wp_get_attachment_image_sizes' ) ? wp_get_attachment_image_sizes( $thumbnail_id, $small_thumbnail_size ) : false;
} else {
$image = wc_placeholder_img_src();
$image_srcset = $image_sizes = false;
}
There is more regarding product thumbnail in the woocommerce code.
Any help?