Symantec Endpoint Protection (SEP) clients fail to obtain content from Group Update Providers (GUPs) over slow wide-area network (WAN) links
GUPs incorrectly handle the http response code 400 from the SEPM which causes content corruption.
This issue is resolved in Symantec Endpoint Protection (SEP) 14.0 MP2. For more information on upgrading, please see Upgrade or migrate to Endpoint Protection 14
To workaround the issue:
Edit httpd.conf from %SEPM%/apache/conf/httpd.conf
ConnectionsToQueuePerChild 3000 (default value 500)