there are a couple of fix ID's available for this in SEPM 12.1.6 MP1, so I would suggest you to upgrade to SEPM 12.1.6 MP3 which also fixes critical security vulnerabilities
In SEPM, Linux clients always show definitions are not available
Fix ID: 3689583
Symptom: In Symantec Endpoint Protection Manager 12.1.5 or 12.1.6, under Clients > Clients > Default view, you see that definitions display as “Not Available” for any Symantec Endpoint Protection client for Linux. This incorrect status remains even after the client downloads new definitions.
Solution: Modified SQL to ensure that it properly handles and cleans up the pattern for existing clients in order to display the correct status for Linux clients.
After upgrading to 12.1.5, SEPM Virus Definition column displays “Not Available”
Fix ID: 3783939
Symptom: After you upgrade Symantec Endpoint Protection Manager to 12.1.5 and then click Clients > Group > Clients > Default View, the Virus Definition column displays “Not Available”. The log file vpdebug.log also shows the following error: Unable to retrieve ISavInfo2. Code 0x80040154
Solution: Changed the context so that virus definitions can correctly register with the component services.
New fixes in Symantec Endpoint Protection 12.1.6 MP1a and 12.1.6 MP1