Most review comments addressed

Author: Extrys

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

@@ -3244,6 +3244,8 @@ internal static NetworkObject AddSceneObject(in SceneObject sceneObject, FastBuf
             //Attempt to create a local NetworkObject
             var networkObject = networkManager.SpawnManager.CreateLocalNetworkObject(sceneObject, instantiationDataReader);
 
+            instantiationDataReader.Dispose();
+
             if (networkObject == null)
             {
                 // Log the error that the NetworkObject failed to construct

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

@@ -120,7 +120,7 @@ public bool AddHandler(uint globalObjectIdHash, INetworkPrefabInstanceHandler in
         public void SetInstantiationData<T>(GameObject gameObject, T instantiationData) where T : struct, INetworkSerializable
         {
             if (gameObject.TryGetComponent<NetworkObject>(out var networkObject))
-                SetInstantiationData(networkObject,instantiationData);
+                SetInstantiationData(networkObject, instantiationData);
         }
         public void SetInstantiationData<T>(NetworkObject networkObject, T data) where T : struct, INetworkSerializable
         {
@@ -238,7 +238,7 @@ public bool RemoveHandler(uint globalObjectIdHash)
                 m_PrefabInstanceToPrefabAsset.Remove(networkPrefabHashKey);
             }
 
-            if(m_PrefabAssetToPrefabHandlerWithData.TryGetValue(globalObjectIdHash, out var handlerWithData))
+            if (m_PrefabAssetToPrefabHandlerWithData.TryGetValue(globalObjectIdHash, out var handlerWithData))
             {
                 m_PrefabAssetToPrefabHandlerWithData.Remove(globalObjectIdHash);
             }
@@ -296,11 +296,7 @@ internal FastBufferReader GetInstantiationDataReader(uint objectHash, FastBuffer
 
             fastBufferReader.ReadValueSafe(out int dataSize);
             int dataStartPos = fastBufferReader.Position;
-            unsafe
-            {
-                byte* ptr = fastBufferReader.GetUnsafePtr() + dataStartPos;
-                return new FastBufferReader(ptr, Collections.Allocator.None, dataSize);
-            }
+            return new FastBufferReader(fastBufferReader, Collections.Allocator.Temp, dataSize, dataStartPos);
         }
 
         /// <summary>
@@ -343,21 +339,15 @@ internal NetworkObject HandleNetworkPrefabSpawn(uint networkPrefabAssetHash, ulo
             else
             {
                 if (m_PrefabAssetToPrefabHandler.TryGetValue(networkPrefabAssetHash, out var prefabInstanceHandler))
-                    networkObjectInstance  = prefabInstanceHandler.Instantiate(ownerClientId, position, rotation);
+                    networkObjectInstance = prefabInstanceHandler.Instantiate(ownerClientId, position, rotation);
             }
             //Now we must make sure this alternate PrefabAsset spawned in place of the prefab asset with the networkPrefabAssetHash (GlobalObjectIdHash)
             //is registered and linked to the networkPrefabAssetHash so during the HandleNetworkPrefabDestroy process we can identify the alternate prefab asset.
-            if (networkObjectInstance != null)
-                RegisterPrefabInstance(networkObjectInstance, networkPrefabAssetHash);
-            return networkObjectInstance;
-        }
-
-        private void RegisterPrefabInstance(NetworkObject networkObjectInstance, uint networkPrefabAssetHash)
-        {
             if (networkObjectInstance != null && !m_PrefabInstanceToPrefabAsset.ContainsKey(networkObjectInstance.GlobalObjectIdHash))
             {
                 m_PrefabInstanceToPrefabAsset.Add(networkObjectInstance.GlobalObjectIdHash, networkPrefabAssetHash);
             }
+            return networkObjectInstance;
         }
 
         /// <summary>
@@ -403,9 +393,9 @@ public GameObject GetNetworkPrefabOverride(GameObject gameObject)
                     {
                         case NetworkPrefabOverride.Hash:
                         case NetworkPrefabOverride.Prefab:
-                            {
-                                return m_NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].OverridingTargetPrefab;
-                            }
+                        {
+                            return m_NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].OverridingTargetPrefab;
+                        }
                     }
                 }
             }

com.unity.netcode.gameobjects/Runtime/Spawning/INetworkPrefabInstanceHandlerWithData.cs renamed to com.unity.netcode.gameobjects/Runtime/Spawning/NetworkPrefabInstanceHandlerWithData.cs

@@ -19,8 +19,18 @@ public abstract class NetworkPrefabInstanceHandlerWithData<T> : INetworkPrefabIn
 
         NetworkObject INetworkPrefabInstanceHandlerWithData.Instantiate(ulong ownerClientId, Vector3 position, Quaternion rotation, FastBufferReader reader)
         {
+            var startPosition = reader.Position;
             reader.ReadValueSafe(out T _payload);
-            return Instantiate(ownerClientId, position, rotation, _payload);
+            var length = reader.Position - startPosition;
+           
+            NetworkObject networkObject = Instantiate(ownerClientId, position, rotation, _payload);
+            reader.Seek(startPosition);
+            if (networkObject.InstantiationData == null || networkObject.InstantiationData.Length != length)
+            {
+                networkObject.InstantiationData = new byte[length];
+            }
+            reader.ReadBytesSafe(ref networkObject.InstantiationData, length);
+            return networkObject;
         }
 
         NetworkObject INetworkPrefabInstanceHandler.Instantiate(ulong ownerClientId, Vector3 position, Quaternion rotation) => Instantiate(ownerClientId, position, rotation, default);