why do I have so many bugs in my custom networkmanager HUD script

I got many bugs in my custom network manager HUD script and I don't know what is the problem. I think because if a client leaves the server the server doesn't know the client has left. But I have tried many things but I don't know what the problem really is.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.Networking;
 using System.Net;
 using System.Net.Sockets;
 using UnityEngine.SceneManagement;
 using TMPro;
 
 
 public class NetworkManagerHUDCustom : NetworkBehaviour
 {
     public GameObject button1Host;
     public GameObject button2Host;
 
     public GameObject button1Join;
     public GameObject button2Join;
 
     public GameObject canvas;
     public GameObject buttons;
 
     public string ip;
     public string shortIp;
 
     public TMP_Text ipText; 
     public TMP_InputField ipInput;
 
     public bool updateblabla;
     private bool isConnected;
 
     // Runtime variable
     bool m_ShowServer;
 
     public NetworkManager manager;               
 
     void Awake()
     {
         manager = GameObject.FindObjectOfType<NetworkManager>();
         MakeShortIp();
         FirstPartOfIp();
 
         manager = NetworkManager.singleton;
     }
 
     private void Update()
     {
         //manager.IsClientConnected
         if (!ipInput)
         {
             return;
         }
         else
         {
             ip = FirstPartOfIp() + ipInput.text;
         }
 
         if (SceneManager.GetActiveScene().name == "Main")
         {
             canvas.SetActive(true);
             buttons.SetActive(true);
         }
         else
         {
             canvas.SetActive(false);
             buttons.SetActive(false);
         }
     }
 
     public string FirstPartOfIp()
     {
         string localIp = LocalIPAddress();
         while (localIp.Substring(localIp.Length - 1, 1) != ".")
         {
             localIp = localIp.Remove(localIp.Length - 1);
         }
         return (localIp);
     }
 
     public void MakeShortIp()
     {
         string localIp = LocalIPAddress();
         while (localIp.Substring(localIp.Length - 1, 1) != ".")
         {
             shortIp = shortIp.Insert(0, localIp.Substring(localIp.Length - 1, 1));
             localIp = localIp.Remove(localIp.Length - 1);
         }
         ipText.text = shortIp;
     }
 
     public string LocalIPAddress()
     {
         IPHostEntry host;
         string localIP = "";
         host = Dns.GetHostEntry(Dns.GetHostName());
         foreach (IPAddress ip in host.AddressList)
         {
             if (ip.AddressFamily == AddressFamily.InterNetwork)
             {
                 localIP = ip.ToString();
                 break;
             }
         }
         return localIP;
     }
 
     public void HostParty(GameObject button)
     {
         if (!manager.IsClientConnected() && !NetworkServer.active && manager.matchMaker == null)
         {
             if (UnityEngine.Application.platform != RuntimePlatform.WebGLPlayer)
             {
 
                 manager.StartHost();
 
             }
         }
         SwitchButton(button1Host, button2Host);
         button1Join.SetActive(false);
         button2Join.SetActive(false);
     }
 
     public void JoinParty(GameObject button)
     {
         if (!manager.IsClientConnected() && !NetworkServer.active && manager.matchMaker == null)
         {
             manager.networkAddress = ip;
             manager.StartClient();
         }
 
         SwitchButton(button1Join, button2Join);
         button1Host.SetActive(false);
         button2Host.SetActive(false);
     }
 
     public void LeaveParty(GameObject button)
     {
         if (manager.IsClientConnected())
         {
             manager.StopMatchMaker();
             manager.StopClient();
         }
 
         SwitchButton(button2Join, button1Join);
         button1Host.SetActive(true);
         button2Host.SetActive(true);
     }
 
 
     public void StopHostParty(GameObject button)
     {
         if (NetworkServer.active)
         {
             if (manager.IsClientConnected())
             {
                 manager.StopHost();
             }
         }
 
         SwitchButton(button2Host, button1Host);
         button1Join.SetActive(true);
         button2Join.SetActive(true);
     }
 
     public void SwitchButton(GameObject obj1, GameObject obj2)
     {
         obj1.SetActive(false);
         obj2.SetActive(true);
     }
 }