Cannot see all users under Users&Devices

Hi ,

I am using FortiGate 100F.

Firmware version 6.4.9 build1966 (GA)

under Dashboard ---->Users & Devices , I click on FortiClient Widget.

I can see all my Devices that are online,I can see the mac and ip address under the Address column.But under the User column , i see only couple of users and I don't see most of them.

Any help will be much appreciated.

Thanks

Tazio