multisite - Cookie signed verification failed - wp-saving-post

I'm setting a WordPress, but posts can't be saved. A 500 error shows up. I contacted the system's team, and apparently it's because they have a Firewall (Fortiweb), and one of the rules is about cookie security.

The Firewall is returning the error:

Cookie signed verification failed - Cookie name (wp-signed-post), signed verification failed;

It's a WordPress Multisite, working with HTTPS and I added in the wp-config.php:

define('ADMIN_COOKIE_PATH', '/');
define('COOKIE_DOMAIN', '');
define('COOKIEPATH', '');
define('SITECOOKIEPATH', '');

I also tried to change the cookie domain with:

define('COOKIE_DOMAIN', $_SERVER['HTTP_HOST']);

How can I deal with it?

Thank you!