Hided products counted in products per page

Under “Products” and “Inventory” I have checked the following setting:
“Hide out of stock items from the catalog”

Now all sold out products are hidden. So far so good.

Then I wanted to change how many products that are visible each page (9 products, 3 each row). So I added the following code to my functions.php:

add_filter( 'loop_shop_per_page', create_function( '$cols', 'return 9;' ), 20 );

add_filter('loop_shop_columns', 'loop_columns');
if (!function_exists('loop_columns')) {
function loop_columns() {
return 3; // 3 products per row
}
}

The problem here is that the hidden (out of stock) products are counted per page. So if there are 3 products that are sold out on the first page, only the ones in stock are showing (6).

Any ideas how to fix this?

https://wordpress.org/plugins/woocommerce/