You may see the Cisco ASA Firewall whose interfaces are described as "Adaptive security Appliance MZ interface" show 0% for interface utilization. When Technical Support collects the attributes polled by Spectrum using SSLogger, it finds from the output that the interface utilization is less than 1%.
The reason 0% utilization is displayed for the interfaces is because the utilization is between 0% and 1% (if the utilization is below 1%, Spectrum will report it as 0%). For example, from SSlogger output if attribute 0x10e41 (ifInOctets) shows a variation of 266 (201348976 - 201348710) on a gigabit interface Spectrum will report the interface utilization as 0%. (In a gigabit interface, 266 octets << 1%)