ProxySG appliances in datacenters provide the Blue Coat Security Service (cloud), which means they use the same BCWF (Blue Coat Web Filter) database and DRTR (Dynamic Rating). It is not good practice to block the Unrated category unless you understand exactly what that means.
The result is expected. If you do not have SSL Intercept enabled in the cloud service, it will rate the IP address of the destination; if it is unrated, the block occurs.
1) Unblock the Unrated category as it will block all sites that have not been rated by BCWF database.
2) Keep the Unrated category blocked and add a rule to override (allow) any legitimate website that you want to allow, such as You Tube, Google, Soundcloud, Yahoo and so on.
NOTE: This requires that you maintain the list of legitimate websites.