Strange Ping problem.

Hi I have FortiGate 200D with V,5.6.8,

When I ping IP address (Its public DNS server IP) from my PC I Get :Destination host unreachable.

When I try to ping connected directly to the router - all good.

When I ping from the FortiGate CLI - all good.

I try few random IP addresses from my PC and - all good

Why and How it block this address!? and maybe more I don't know of. 

I have no idea where to check.