WordPress sends a request to wp-cron.php to get this loopback info. However, as a security precaution, we are blocking access to wp-cron.php. So nginx returns a 403 response when WordPress sends that request. That’s why you’re seeing this loopback issue along with the page cache header. You can ignore this error, nothing to worry about. We trigger cron every 10 minutes via wp-cli, so your cron is executing perfectly, no issues there.