Hi,
If it's a SEPM 12.1 RU2 or any prior version of the SEPM then it can be a known issue.
Go through the following fix id, listed in RU2 MP1 fix notes:
LiveUpdate is unable to decompress the virus definition updates despite ample room on the system
Fix ID: 2847004
Symptom: Symantec Endpoint Protection client will run LiveUpdate and successfully download updated content, but occasionally cannot apply the updates. “Decompression failed for package…” errors appear in the lue.log files.
Solution: The updated LiveUpdate Express included in RU2 MP1 updates the decompression process to use less memory, which allows the extraction to occur.
Reference: New fixes and features in Symantec Endpoint Protection 12.1 Release Update 2 Maintenance Pack 1
I would recommend to upgrade to the most latest version of SEPM i.e. SEPM 12.1 RU4a to stay more protected.