It's definitely possible that the traffic never reaches your Fortigate. It's also possible the traffic matched a pre-existing session that is offloaded into NPx (if equipped).
// check for existing sessions (that are may be offloaded)
diag sys session filter clear
diag sys session filter dst 192.168.0.38
diag sys session filter dport 80
diag sys session list
// clear existing sessions if they exist
NOTE: Ensure to specify the above session filters so that you do not accidentally clear all your sessions :-).
diag sys session clear
You can also double check by capturing the traffic with the bellow CLI command:
diag sniff packet any 'host <WAN1_IP_Address> and port 80' 4
If there are no established sessions and no output is generated by the sniffer/debug, then your Fortigate is not receiving the traffic and you should troubleshoot upstream.