Clients are missing the green dot and are not receiving policy updates from the Symantec Endpoint Protection Manager, but they do show up with a green dot in the SEPM.
Sylink.log generated by a client shows the following error:
04/30 10:49:47 
The wrong server certificate (JKS) has been applied after a Disaster Recovery or reinstall of the Symantec Endpoint Protection Manager.
Follow this document first:
Symantec Endpoint Protection Signature verification FAILED for Index File Content
If it doesn't resolve the issue then follow these steps:
Import the correct server certificate (JKS) into the SEPM.
1.Login to the SEPM
2.Click the Admin button - Select Servers and click on the server name (under Local Site)
3.Under Tasks - Click Manage Server Certificate
4.Choose "Update the server certificate" - choose the certificate type (.JKS) - Locate and select the correct .JKS file to restore.
(Note: The password is the same for both password fields and can be found next to the KeyStorePass= line in the corresponding .xml file to the .JKS you are restoring from. Typically under %Program Files%\Symantec\Symantec Endpoint Protection Manager\Sever Private Key Backup\ or in the location where you keep them.)
Once the certificate has been restored, restart the SEPM service for the changes to take effect. As the clients check in they will start to communicate with the SEPM successfully.