fix

Adding the back to back network  show and change ownership message fix.
Adding the client synchronization network show fix.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -35,6 +35,15 @@ public void Handle(ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
+
+            // Sanity check that we are not sending duplicated or unnecessary change ownership messages
+            if (networkObject.OwnerClientId == OwnerClientId)
+            {
+                // Log error and then ignore the message
+                NetworkLog.LogError($"[Receiver: Client-{networkManager.LocalClientId}][Sender: Client-{context.SenderId}] Detected unnecessary ownership changed message for {networkObject.name} (NID:{NetworkObjectId}).");
+                return;
+            }
+
             var originalOwner = networkObject.OwnerClientId;
 
             networkObject.OwnerClientId = OwnerClientId;

com.unity.netcode.gameobjects/Runtime/SceneManagement/SceneEventData.cs

@@ -317,6 +317,12 @@ internal void AddSpawnedNetworkObjects()
             m_NetworkObjectsSync.Clear();
             foreach (var sobj in m_NetworkManager.SpawnManager.SpawnedObjectsList)
             {
+                var spawnedObject = sobj;
+                // Don't synchronize objects that have pending visibility as that will be sent as a CreateObjectMessage towards the end of the current frame
+                if (TargetClientId != NetworkManager.ServerClientId && m_NetworkManager.SpawnManager.IsObjectVisibilityPending(TargetClientId, ref spawnedObject))
+                {
+                    continue;
+                }
                 if (sobj.Observers.Contains(TargetClientId))
                 {
                     m_NetworkObjectsSync.Add(sobj);

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

@@ -321,6 +321,10 @@ internal void ChangeOwnership(NetworkObject networkObject, ulong clientId)
 
             foreach (var client in NetworkManager.ConnectedClients)
             {
+                if (IsObjectVisibilityPending(client.Key, ref networkObject))
+                {
+                    continue;
+                }
                 if (networkObject.IsNetworkVisibleTo(client.Value.ClientId))
                 {
                     var size = NetworkManager.ConnectionManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, client.Value.ClientId);
@@ -343,6 +347,23 @@ internal void ChangeOwnership(NetworkObject networkObject, ulong clientId)
             m_LastChangeInOwnership[networkObject.NetworkObjectId] = Time.realtimeSinceStartup + (tickFrequency * k_MaximumTickOwnershipChangeMultiplier);
         }
 
+        /// <summary>
+        /// Will determine if a client has been granted visibility for a NetworkObject but
+        /// the <see cref="CreateObjectMessage"/> has yet to be generated for it. Under this case,
+        /// the client might not need to be sent a message (i.e. <see cref="ChangeOwnershipMessage")
+        /// </summary>
+        /// <param name="clientId">the client to check</param>
+        /// <param name="networkObject">the <see cref="NetworkObject"/> to check if it is pending show</param>
+        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
+        internal bool IsObjectVisibilityPending(ulong clientId, ref NetworkObject networkObject)
+        {
+            if (ObjectsToShowToClient.ContainsKey(clientId))
+            {
+                return ObjectsToShowToClient[clientId].Contains(networkObject);
+            }
+            return false;
+        }
+
         internal bool HasPrefab(NetworkObject.SceneObject sceneObject)
         {
             if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.IsSceneObject)