fix

This fixes most of the synchronization issues with using a distributed authority network topology and scene management is disabled.
(There still is some form of issue with changing ownership when distributing objects)

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Connection/NetworkConnectionManager.cs

@@ -1001,6 +1001,14 @@ internal NetworkClient AddClient(ulong clientId)
             }
 
             var distributedAuthority = NetworkManager.DistributedAuthorityMode;
+
+            // If not using DA return early or if using DA and scene management is disabled then exit early Since we use NetworkShow to spawn
+            // objects on the newly connected client side.
+            if (!distributedAuthority || distributedAuthority && !NetworkManager.NetworkConfig.EnableSceneManagement)
+            {
+                return networkClient;
+            }
+
             var sessionOwnerId = NetworkManager.CurrentSessionOwner;
             var isSessionOwner = NetworkManager.LocalClient.IsSessionOwner;
             foreach (var networkObject in NetworkManager.SpawnManager.SpawnedObjectsList)

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

@@ -2894,7 +2894,7 @@ internal SceneObject GetMessageSceneObject(ulong targetClientId = NetworkManager
                 SyncObservers = syncObservers,
                 Observers = syncObservers ? Observers.ToArray() : null,
                 NetworkSceneHandle = NetworkSceneHandle,
-                Hash = HostCheckForGlobalObjectIdHashOverride(),
+                Hash = CheckForGlobalObjectIdHashOverride(),
                 OwnerObject = this,
                 TargetClientId = targetClientId
             };
@@ -3246,14 +3246,14 @@ internal void UpdateForSceneChanges()
         }
 
         /// <summary>
-        /// Only applies to Host mode.
+        /// Only applies to Hosts or session owners (for now)
         /// Will return the registered source NetworkPrefab's GlobalObjectIdHash if one exists.
         /// Server and Clients will always return the NetworkObject's GlobalObjectIdHash.
         /// </summary>
-        /// <returns></returns>
-        internal uint HostCheckForGlobalObjectIdHashOverride()
+        /// <returns>appropriate hash value</returns>
+        internal uint CheckForGlobalObjectIdHashOverride()
         {
-            if (NetworkManager.IsServer)
+            if (NetworkManager.IsServer || (NetworkManager.DistributedAuthorityMode && NetworkManager.LocalClient.IsSessionOwner))
             {
                 if (NetworkManager.PrefabHandler.ContainsHandler(this))
                 {

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

@@ -332,7 +332,7 @@ private void HandleOwnershipChange(ref NetworkContext context)
             // Sanity check that we are not sending duplicated change ownership messages
             if (networkObject.OwnerClientId == OwnerClientId)
             {
-                UnityEngine.Debug.LogError($"Unnecessary ownership changed message for {NetworkObjectId}.");
+                UnityEngine.Debug.LogError($"Client-{context.SenderId} sent unnecessary ownership changed message for {NetworkObjectId}.");
                 // Ignore the message
                 return;
             }

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

@@ -55,19 +55,23 @@ public void Handle(ref NetworkContext context)
                 // Don't redistribute for the local instance
                 if (ClientId != networkManager.LocalClientId)
                 {
+                    // Synchronize the client with spawned objects (relative to each client)
+                    networkManager.SpawnManager.SynchronizeObjectsToNewlyJoinedClient(ClientId);
+
+                    // Keeping for reference in case the above doesn't resolve for hidden objects (theoretically it should)
                     // Show any NetworkObjects that are:
                     // - Hidden from the session owner
                     // - Owned by this client
                     // - Has NetworkObject.SpawnWithObservers set to true (the default)
-                    if (!networkManager.LocalClient.IsSessionOwner)
-                    {
-                        networkManager.SpawnManager.ShowHiddenObjectsToNewlyJoinedClient(ClientId);
-                    }
+                    //if (!networkManager.LocalClient.IsSessionOwner)
+                    //{
+                    //    networkManager.SpawnManager.ShowHiddenObjectsToNewlyJoinedClient(ClientId);
+                    //}
 
                     // We defer redistribution to the end of the NetworkUpdateStage.PostLateUpdate
                     networkManager.RedistributeToClient = true;
                     networkManager.ClientToRedistribute = ClientId;
-                    networkManager.TickToRedistribute = networkManager.ServerTime.Tick + 20;
+                    networkManager.TickToRedistribute = networkManager.ServerTime.Tick + (int)(0.5f * networkManager.NetworkConfig.TickRate);
                 }
             }
         }

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

@@ -580,7 +580,6 @@ internal void ChangeOwnership(NetworkObject networkObject, ulong clientId, bool
                     {
                         networkObject.ChildNetworkBehaviours[i].UpdateNetworkProperties();
                     }
-
                     size = NetworkManager.ConnectionManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ServerClientId);
                     NetworkManager.NetworkMetrics.TrackOwnershipChangeSent(NetworkManager.LocalClientId, networkObject, size);
                 }
@@ -1976,14 +1975,14 @@ internal void NotifyNetworkObjectsSynchronized()
         /// synchronizing in order to "show" (spawn) anything that might be currently hidden from
         /// the session owner.
         /// </summary>
+        /// <remarks>
+        /// Replacement is: SynchronizeObjectsToNewlyJoinedClient
+        /// </remarks>
         internal void ShowHiddenObjectsToNewlyJoinedClient(ulong newClientId)
         {
-            if (!NetworkManager.DistributedAuthorityMode)
+            if (NetworkManager == null || NetworkManager.ShutdownInProgress && NetworkManager.LogLevel <= LogLevel.Developer)
             {
-                if (NetworkManager == null || !NetworkManager.ShutdownInProgress && NetworkManager.LogLevel <= LogLevel.Developer)
-                {
-                    Debug.LogWarning($"[Internal Error] {nameof(ShowHiddenObjectsToNewlyJoinedClient)} invoked while !");
-                }
+                Debug.LogWarning($"[Internal Error] {nameof(ShowHiddenObjectsToNewlyJoinedClient)} invoked while shutdown is in progress!");
                 return;
             }
 
@@ -2019,5 +2018,46 @@ internal void ShowHiddenObjectsToNewlyJoinedClient(ulong newClientId)
                 }
             }
         }
+
+        internal void SynchronizeObjectsToNewlyJoinedClient(ulong newClientId)
+        {
+            if (NetworkManager == null || NetworkManager.ShutdownInProgress && NetworkManager.LogLevel <= LogLevel.Developer)
+            {
+                Debug.LogWarning($"[Internal Error] {nameof(SynchronizeObjectsToNewlyJoinedClient)} invoked while shutdown is in progress!");
+                return;
+            }
+
+            if (!NetworkManager.DistributedAuthorityMode)
+            {
+                Debug.LogError($"[Internal Error] {nameof(SynchronizeObjectsToNewlyJoinedClient)} should only be invoked when using a distributed authority network topology!");
+                return;
+            }
+
+            if (NetworkManager.NetworkConfig.EnableSceneManagement)
+            {
+                Debug.LogError($"[Internal Error] {nameof(SynchronizeObjectsToNewlyJoinedClient)} should only be invoked when scene management is disabled!");
+                return;
+            }
+
+            var localClientId = NetworkManager.LocalClient.ClientId;
+            foreach (var networkObject in SpawnedObjectsList)
+            {
+                if (networkObject.SpawnWithObservers && networkObject.OwnerClientId == localClientId)
+                {
+                    if (networkObject.Observers.Contains(newClientId))
+                    {
+                        if (NetworkManager.LogLevel <= LogLevel.Developer)
+                        {
+                            // Temporary tracking to make sure we are not showing something already visibile (should never be the case for this)
+                            Debug.LogWarning($"[{nameof(SynchronizeObjectsToNewlyJoinedClient)}][{networkObject.name}] New client as already an observer!");
+                        }
+                        // For now, remove the client (impossible for the new client to have an instance since the session owner doesn't) to make sure newly added
+                        // code to handle this edge case works.
+                        networkObject.Observers.Remove(newClientId);
+                    }
+                    networkObject.NetworkShow(newClientId);
+                }
+            }
+        }
     }
 }