When editing a Policy though Management Center following error is reported when hovering mouse pointer over it:
"WSS only supports logging to Main"
Also "Save Policy" button is greyed out preventing from save the policy.
It's related to policy enforcement, only "Appliance" enforcement can log to non-main log file.
WSS (Cloud SWG) does not support logging to non-main log files.
Resolution is to change Enforcement from "Universal" to "Appliance"