SyncListString not changing properly

Hey, I tried to keep track of all users in my multiplayer game, but when I try to assign new names (string) to the List it will only have the own names in it. I am kinda confused, because it also happend to normal [SyncVar] strings.

T$$anonymous$$s is my code:

 public class PlayerManager : NetworkBehaviour
 {
     public SyncListString Users;
 
     // Use t$$anonymous$$s for initialization
     void Start()
     {
         if (t$$anonymous$$s.isLocalPlayer) CmdNameToServer();
     }
 
     [Command]
     public void CmdNameToServer()
     {
         Debug.LogError("Server Call");
         string newname = "Player " + Random.Range(1, 100);
         Users.Add(newname + "Server");
         RpcNameToClients(newname);
 
     }
     [ClientRpc]
     public void RpcNameToClients(string newname)
     {
         Debug.LogError("Client Call");
         Users.Add(newname + "Client");
         Debug.LogError(Users.Count);
     }
 }

I am using Unity the latest release of Unity, in my case it is 2018.2.0b1.

Thanks for any kind of help!

-Twenty