Fortigate 5.6 and explicit proxy

Hi there,

I'm facing a problem that is driving me mad.

I have a FG 3240C running FortiOS 5.6.14 with different VDOMS configured in it, there I have configured an explicit proxy that is needed for some subnet not directly connected to me.

For years everithing was working fine, but now some client has started receiving the block page:

"Access Denied - the page you requested has been blocked by a firewall policy restriction".

I tried to make troubleshooting following guides I have found online, like the one below:

https://community.fortinet.com/t5/FortiGate/Technical-note-WAD-troubleshooting-commands/ta-p/195183?externalID=FD42352

There in no output  from the commands:

Fortigate-A (vdom3) # diagnose wad user list

Fortigate-A (vdom3) # diagnose wad session list

Sessions total=0

and the "diag wad debug" commands  didn't show the IP of the PCs receiving the block, so I still can't understand the reason of this behaviuor.

I hope somebody can help me. :)

Thanks in advance.