FG30E - restrict youtube not working

Hi there,

kindly please help.

I've created policy, with setting:

- enable NAT

- enable web filter, with web filter's setting: 

- restrict youtube access

- enable fortigate category based filter using default setting.

I try to every computers, they can access youtube via web browser.

I'm using FG30E with firmware v6.0.11 build0387 (GA). and network topology is:

Internet - Fortigate - Wifi Router - client.

try to connect from fortigate to LAN port or Internet Port on wifi router, still get same result, client can access youtube.

kindly please help how to block access youtube effectively.

moreover, both from web browser or from application.

thank you