Users that get blocked from an event by a CASB\DLP Gatelet policy want to see a pop-up notification explaining that the event was block because of a policy violation.
The WSSAgent does have the ability to provide a pop-up notification that the block occurred because of a violation. (Contact Support to get BNS Block Notfications enabled)
CASB customer's steering Gateway traffic via Proxy Forwarding from the local proxy or WSS-SEP_NTR, both do not have the ability to provide a pop-up notification. The block takes place after the local proxy and WSS has finished forwarding the data.
The Broadcom product team is looking to enhance the product in the future. A support ticket with the organization details can be added to the Feature Request. The Feature Request number is ISFR-1654