You have posted this in the Endpoint Encryption forums, by mistake. I'd recommend you amend this to the Endpoint Protection forums instead.
To your question though, and assuming that you've already checked out the LUA itself and that everything is fine, then you'll need to check the LiveUpdate logs on your RHEL client. These are found at:
- SEP 12.1.x - /opt/Symantec/LiveUpdate/liveupdt.log
- SEP 14 and newer - /opt/Symantec/LiveUpdate/Logs/lux.log