I had this problem with a few of my costumers.
The Fortigate appliance suddenly decided that legitimate web sites categorized as porno.
At first I filled the form for reevaluate the web sites until is became a flood.
I have opened a ticket at Fortinet for this problem and this is there respond….
Dear customer,
Thank you for contacting Fortinet Technical Support and sorry for the delay in the update.
Follow the below procedure from the GUI:
-Go to UTM >web filter >profile.
-Expand “advanced filter”
-Disable the check box for the option “Rate URLs by Domain and IP Address”.
Hope it helps.