Fortinet IPS does not block Joomla!.Core.Account.Creation.Privilege.Escalation Exploit

Dear All,

I have deployed Fortigate VM in AWS and all the licenses are active except Fortiguard. My issue is when I do a exploit to Joomla 3.4.4 instance placed behind the Fortigate VM through a Security Policy which has a IPS profile with all the IPS signatures selected, it does not get blocked, exploit success and user gets created on the Joomla instance.

I have no idea why Fortigate does not block that exploit attempt. And also I can find that specific signature in the IPS Signature database in my instance.