Check your connection events. (Analysis > Connections > Events). In case you cannot find the specific event, make sure logging is enabled for your access-control-policy rules and the time interval in the events view is set correctly (default = 60 minutes, which can be adjusted by using the clock link on the top right).
Per default the table will not include all fields (like matching rule). To overcome this limitation click on a field you would like to filter on. The page will reload and you can view which rule matched the traffic.
