Open a case wth Symantec Support. The issue is fixed in SEPM RU6
Kindly find the below details..
Apache process crashes, clients reporting offline after SEPM upgrade
FIX ID: 3680595, 3682969, 3721675
Symptom: In environments with large numbers of content definition downloads, httpd.exe crashes.
Solution: Fixed the logic in the high-performance file download routines for Symantec Endpoint Protection Manager’s httpd.exe implementation.
Note:- Symantec Technical Engineer will provide workaround