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If anyone has the same problem.

Check the headers sent by the CDN

print_r($_SERVER)

find out in what header they send the visitor's IP and change the value of $_SERVER['REMOTE_ADDR'] and $_SERVER['HTTP_X_FORWARDED_FOR'] with the actual IP at the top of your code (for exemple config/config.inc.php) 

Quote

if (isset($_SERVER['IP_SENT_BY_CDN']) && $_SERVER['IP_SENT_BY_CDN']!='') {
    //$_SERVER['HTTP_X_FORWARDED_FOR'] = $_SERVER['IP_SENT_BY_CDN'];
    $_SERVER['REMOTE_ADDR'] = $_SERVER['IP_SENT_BY_CDN'];
}

This might solve it.