Network connecting makes GUI work weirdly

Hi,everyone. I had some problem about network connecting. This is the scene and you can click the button to connect server. And the server is another project and I built it before. The problem is when I click the button it won't call the function 'OnNetworkLoaded' immediately. When I focus on the server window (another project), and back to client window, it works. If I don't focus on the server window, the function doesn't be called. But it connect the server normally.

And more, when I restart my computer, it works normally... one or two times.

Did I do something wrong? Thank you all for reading my problem.

     private string remoteIP = "127.0.0.1";
     private int listenPort = 10000;
     private bool useNAT = false;
 
     void OnConnectedToServer(){
         foreach(GameObject go in FindObjectsOfType(typeof(GameObject)))
         {
             go.SendMessage("OnNetworkLoaded",SendMessageOptions.DontRequireReceiver);
         }
     }
 
     void OnGUI() {
 
         switch (Network.peerType) {
             
         case NetworkPeerType.Disconnected:
             StartConnect();
             break;
 
         case NetworkPeerType.Client:
             ClientTo();
             break;
 
         case NetworkPeerType.Connecting:
             Debug.Log ("Connecting...");
             break;
         }
 
     }
 
     void StartConnect() {
 
         if (GUI.Button (new Rect (10, 50, 100, 30), "Connect Server")) {
 
             Debug.Log ("Onbutton");
 
             NetworkConnectionError error = Network.Connect(remoteIP,listenPort,"UnityNetwork");
             Debug.Log(error);
 
         }
     }
 
     void ClientTo(){
         GUILayout.Label ("Succeed");
     }