Some Clients are not listed in the Endpoint protection Manager

Hi Guys,

We have installed Symantec Endpoint Protection 12.1.3 on Server 2012 R2. I installed symantec installation client to workstation and it was installed and works fine in client Pcs but it is not listed in the Symantec Endpoint Protection Manager Clients tab. Some workstations are listed but most of them are not listed. Please assist me on this matter. Thanks in advance.