Open a technical support ticket with the CASB (CloudSOC) support team and have them enable the "Activate WSS Sync" feature in the CASB BOP (back office portal).
In the CASB BOP, go to: "Gateway | Features" and enable the checkbox:
"Activate WSS Sync"
NOTE: currently, starting the initial sync of CASB gatelets between WSS and CASB is a manual process that can only be done by a CASB/CloudSOC support engineer.