Error on specific product

I get the following json as a response on a specific product:

{“version”:”20210604″,”show_thumbnails”:false,”show_date”:true,”show_context”:true,”layout”:”grid”,”headline”:”\u03a3\u03c7\u03b5\u03c4\u03b9\u03ba\u03ac”,”items”:[]}

and only that, no html,css,js etc.
When i manually purge the cache it work like it should. After a while the error comes back up. I used the exclude url but nothing changes.

This product uses a custom template an the code used is:

function single_product_custom($template)
{
if (is_singular(‘product’) && get_the_ID() == xxxx) {
$template = get_stylesheet_directory() . ‘/single-product-custom.php’;
}
return $template;
}

add_filter(‘template_include’, ‘single_product_custom’, 50, 1);

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