Clients cannot send data back to Symantec Endpoint Protection Manager
Browse to \Program Files\Symantec\Symantec Endpoint Protection Manager\data\outbox\agentinfo
2. Look for any .err files or tmp files & Dat files
3. If you find anything which is not processed by sepm then it might be the reason for the client data loss
4. Stop SEPM services from services.msc
5. Delete all the files inside the location \Program Files\Symantec\Symantec Endpoint Protection Manager\data\inbox\agentinfo
6. Restart the SEPM services.