After exporting an installation package for Symantec Endpoint Protection (SEP) and installing that client, the client attempts to use HTTP port 80 for communication instead of port 8014. If you push out a new sylink/communication update package for the same group the package was created for the issue is resolved.
By default the Management Server List (MSL) does not have an HTTP port configured and when creating an installation package the port that is set in that package is port 80 instead of the Symantec Endpoint Protection Manager (SEPM) default of 8014. However when exporting a sylink or communication update package for the same group that port is defined as 8014.
This issue is under investigation and will be resolved in a future version of the Symantec Endpoint Protection Manager.
As a workaround, edit your MSL(s) and define the HTTP port as 8014 or the custom port you've configured and reexport your installation packages so they contain the proper setting.
For clients that were already deployed and are not communicating due to this, you can push out a communication update package as outlined in the following KB:
Restoring client-server communications with Communication Update Package Deployment
CRE-17686