fix: spawn a NetworkObject shown after a scene migration in the server's scene

A client that starts observing a NetworkObject with NetworkShow after the NetworkObject migrated into another scene was never sent that migration, and instantiated the NetworkObject in its active scene. The client now moves a spawned NetworkObject into its server-side scene, as it already does for NetworkObjects that are part of its initial synchronization.

Adds CHANGELOG entries for this and for scene migrations being sent to clients that do not observe the NetworkObject.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -18,6 +18,9 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Issue where moving a `NetworkObject` into another scene made the clients that did not observe it log "Trying to synchronize NetworkObjectId but it was not spawned". The scene migration is now only sent to the clients that observe the `NetworkObject`.
+- Issue where a `NetworkObject` that was moved into another scene while hidden from a client spawned in that client's active scene when it was shown with `NetworkShow`, instead of the scene it is in on the server.
+
 ### Security
 
 ### Obsolete

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

@@ -197,6 +197,13 @@ internal static void CreateObject(ref NetworkManager networkManager, ulong sende
                         networkManager.Log.ErrorServer(new Context(LogLevel.Developer, $"Failed to deserialize {nameof(NetworkObject)}.").AddInfo(nameof(NetworkObject.GlobalObjectIdHash), serializedObject.Hash).AddInfo(nameof(NetworkObject.NetworkObjectId), serializedObject.NetworkObjectId));
                         return;
                     }
+
+                    // A NetworkObject shown to this client after it migrated into another scene was instantiated in the
+                    // active scene, and the migration was only sent to the clients observing it at the time.
+                    if (networkManager.NetworkConfig.EnableSceneManagement)
+                    {
+                        networkManager.SceneManager.SynchronizeNetworkObjectScene(networkObject);
+                    }
                 }
                 else
                 {

com.unity.netcode.gameobjects/Tests/Runtime/NetworkObject/NetworkObjectSceneMigrationObserverTests.cs

@@ -106,6 +106,27 @@ public IEnumerator SceneMigrationWithNoObserversIsNotSent()
             LogAssert.NoUnexpectedReceived();
         }
 
+        /// <summary>
+        /// An object shown to a client after it migrated while hidden from that client spawns in the authority's scene.
+        /// </summary>
+        [UnityTest]
+        public IEnumerator NetworkShowAfterSceneMigrationSpawnsInAuthorityScene()
+        {
+            var authority = GetAuthorityNetworkManager();
+            var client = GetNonAuthorityNetworkManager();
+
+            var networkObject = SpawnObject(m_PrefabNoObserversSpawn, authority).GetComponent<NetworkObject>();
+            yield return s_DefaultWaitForTick;
+            Object.DontDestroyOnLoad(networkObject.gameObject);
+            yield return s_DefaultWaitForTick;
+
+            networkObject.NetworkShow(client.LocalClientId);
+            yield return WaitForSpawnedOn(client, networkObject);
+
+            var clientInstance = client.SpawnManager.SpawnedObjects[networkObject.NetworkObjectId];
+            Assert.AreEqual(client.SceneManager.DontDestroyOnLoadScene, clientInstance.gameObject.scene, $"[Client-{client.LocalClientId}] {networkObject.name} did not spawn in the authority's scene!");
+        }
+
         /// <summary>
         /// A late joining client synchronizes an object that is not in the active scene into the authority's scene.
         /// A hybrid prefab instance can spawn after the synchronization completes, once its ghost arrives.