sc-status is a protocol status code from the appliance to a client. The usual results for sc-status are the following HTTP response codes:
0 (zero) indicates that the ProxySG appliance did not have the chance to send the status code due to a possible connection reset. If you are logging s-action on the same log line, you might see TCP_NC_MISS_RST that could correlated to sc-status 0. A packet capture taken when the sc-status=0 logging is happening can also help.