A sniffer utility (such as Dagsnap, Wireshark, etc.) is capturing traffic but no traffic is being reported through the Monitor UI.
To check the IP Filters from the Enforce UI:
Global: Administration > Settings > Protocols
Server: Administration > Overview > <detection server>. Click Configure tab and select protocol in question.
You can validate whether the IP filters are causing an issue by removing them and then check to see if traffic is being reported through the monitor.
For example, a filter of +,10.67.0.0/16,*;-,*,* matches all IP traffic going to network 10.67.x.x but does not match any other traffic.
For more details on setting up IP Filters, please see KB TECH221378: How to set up IP filters for Vontu Network Monitor
For more information see TECH218779: Endace Card is Not Recognized