fix: Fixed remote disconnects not properly cleaning up

com.unity.netcode.gameobjects/Runtime/Core/NetworkManager.cs

@@ -1291,21 +1291,12 @@ public void DisconnectClient(ulong clientId)
                 throw new NotServerException("Only server can disconnect remote clients. Use StopClient instead.");
             }
 
-            ConnectedClients.Remove(clientId);
-            PendingClients.Remove(clientId);
-
-            for (int i = ConnectedClientsList.Count - 1; i > -1; i--)
-            {
-                if (ConnectedClientsList[i].ClientId == clientId)
-                {
-                    ConnectedClientsList.RemoveAt(i);
-                }
-            }
+            OnClientDisconnectFromServer(clientId);
 
             NetworkConfig.NetworkTransport.DisconnectRemoteClient(clientId);
         }
 
-        internal void OnClientDisconnectFromServer(ulong clientId)
+        private void OnClientDisconnectFromServer(ulong clientId)
         {
             PendingClients.Remove(clientId);
 

com.unity.netcode.gameobjects/Tests/Runtime/DisconnectTests.cs

@@ -0,0 +1,53 @@
+using System.Collections;
+using System.Linq;
+using NUnit.Framework;
+using UnityEngine;
+using UnityEngine.TestTools;
+
+namespace Unity.Netcode.RuntimeTests
+{
+    public class DisconnectTests
+    {
+        [UnityTest]
+        public IEnumerator RemoteDisconnectPlayerObjectCleanup()
+        {
+            // create server and client instances
+            MultiInstanceHelpers.Create(1, out NetworkManager server, out NetworkManager[] clients);
+
+            // create prefab
+            var gameObject = new GameObject("PlayerObject");
+            var networkObject = gameObject.AddComponent<NetworkObject>();
+            networkObject.DontDestroyWithOwner = true;
+            MultiInstanceHelpers.MakeNetworkObjectTestPrefab(networkObject);
+
+            server.NetworkConfig.PlayerPrefab = gameObject;
+
+            for (int i = 0; i < clients.Length; i++)
+            {
+                clients[i].NetworkConfig.PlayerPrefab = gameObject;
+            }
+
+            // start server and connect clients
+            MultiInstanceHelpers.Start(false, server, clients);
+
+            // wait for connection on client side
+            yield return MultiInstanceHelpers.Run(MultiInstanceHelpers.WaitForClientsConnected(clients));
+
+            // wait for connection on server side
+            yield return MultiInstanceHelpers.Run(MultiInstanceHelpers.WaitForClientConnectedToServer(server));
+
+            // disconnect the remote client
+            server.DisconnectClient(clients[0].LocalClientId);
+
+            // wait 1 frame because destroys are delayed
+            var nextFrameNumber = Time.frameCount + 1;
+            yield return new WaitUntil(() => Time.frameCount >= nextFrameNumber);
+
+            // ensure the object was destroyed
+            Assert.False(server.SpawnManager.SpawnedObjects.Any(x => x.Value.IsPlayerObject && x.Value.OwnerClientId == clients[0].LocalClientId));
+
+            // cleanup
+            MultiInstanceHelpers.Destroy();
+        }
+    }
+}