When viewing the report in the Symantec Endpoint Protection Manager (SEPM), Symantec Endpoint Protection (SEP) clients are showing definitions as "Not Available".
If these impacted clients are inspected it is revealed that they do have the latest Virus Definitions present.
Symantec Endpoint Protection 12.1.6 to 12.1.6 MP5
When viewing the report at the SEPM, SEP clients are showing definitions as "Not Available".
Every time CcSvcHst.exe starts up, the PatternFileSequence registry key was getting reset to a zero value. Therefore when the client opstate was sent to the SEPM, the definitions were reported as a null value. This caused the Not Available presence in the report.