Did you pass the correct rule name as a user name (and password, if required) when opening the web-report page?
Also, if that rule uses tracking per IP address or MAC address, the usage will only be shown when requested by the corresponding address.
For example, if it is a tracking rule and has two streams — 188.8.131.52 and 184.108.40.206, then:
if 220.127.116.11 opens this page and supplies the rule name, they will see their own usage;
if 18.104.22.168 opens this page and supplies the rule name, they will see their own usage;
if any other address requests the usage page, nothing will be shown.