NullReferenceException in SceneEventData.DeserializeScenePlacedObjects() when NetworkObject.Deserialize returns null

[AliasgarBohra]

Description

NullReferenceException is thrown in SceneEventData.DeserializeScenePlacedObjects() when NetworkObject.Deserialize() returns null for an in-scene placed NetworkObject during scene synchronization. The null is added to a list without a check, and then InternalInSceneNetworkObjectsSpawned() is called on it, crashing and aborting the entire scene sync for that client.

Reproduce Steps

1. Host or start a server with a scene containing multiple in-scene placed NetworkObjects
2. Have a client connect and load the scene (can also occur on a Load scene event during gameplay)
3. Under certain timing/race conditions, NetworkObject.Deserialize() returns null for one of the in-scene placed NetworkObjects (e.g., when GetSceneRelativeInSceneNetworkObject fails to find the object by GlobalObjectIdHash on the client at sync time)
4. The null reference is added to the sceneObjects list without a null check
5. The foreach loop calls networkObject.InternalInSceneNetworkObjectsSpawned() on the null entry → NullReferenceException

The issue is intermittent — it does not happen every time. It occurs randomly across different game modes and scenes, but once it triggers, the client's scene is permanently broken.

Actual Outcome

NullReferenceException: Object reference not set to an instance of an object
Unity.Netcode.SceneEventData.DeserializeScenePlacedObjects () (at Library/PackageCache/com.unity.netcode.gameobjects@aaabf07f880c/Runtime/SceneManagement/SceneEventData.cs:895)

The exception aborts DeserializeScenePlacedObjects mid-loop. Remaining in-scene placed NetworkObjects never get spawned. The client ends up in a corrupted state:

• In-scene NetworkObjects are missing or partially spawned
• Player spawns fail for that client
• The scene is broken with no recovery path short of reconnecting

Expected Outcome

If NetworkObject.Deserialize() returns null for a specific in-scene placed NetworkObject, that entry should be skipped (not added to the sceneObjects list). The remaining in-scene placed NetworkObjects should continue to synchronize normally. No NullReferenceException should be thrown.

Screenshots

N/A — error is in console/log output only.

Environment

• OS: Windows 11
• Unity Version: 6000.3.19
• Netcode Version: 2.12.0
• Netcode Commit: aaabf07f880c (package hash from PackageCache)
• Netcode Topology: Client-Server

Additional Context

Root cause is in SceneEventData.DeserializeScenePlacedObjects():

// Line 881: Deserialize can return null
var networkObject = NetworkObject.Deserialize(serializedObject, InternalBuffer, m_NetworkManager);

// Line 883-886: BUG — no null check before adding to list
if (serializedObject.IsSceneObject)
{
    sceneObjects.Add(networkObject);  // networkObject can be null here
}

// Line 893-896: Crashes on null
foreach (var networkObject in sceneObjects)
{
    networkObject.InternalInSceneNetworkObjectsSpawned();  // NullReferenceException
}

NetworkObject.Deserialize() returns null in several cases:

• NonAuthorityLocalSpawn fails (line 1217-1218: duplicate NetworkObjectId → returns null)
• CreateLocalNetworkObject returns null (line 978-985: GetSceneRelativeInSceneNetworkObject fails to find the in-scene object by hash)
• SpawnNetworkObjectLocallyCommon returns false (line 1284-1288)

None of these null returns are guarded before being added to sceneObjects.

Suggested fix (one-line change):

// Change line 883 from:
if (serializedObject.IsSceneObject)

// To:
if (serializedObject.IsSceneObject && networkObject != null)

This prevents null entries from entering the list, allowing the rest of the scene sync to complete normally.

Note: This issue was previously reported as #3795 but was closed as stale without a fix. It is still reproducible in 2.12.0 and is not addressed in 2.13.0. The impact is severe — a single failed object deserialization corrupts the entire client scene state with no recovery.

[EmandM]

Thank you for reporting this! This was fixed in #4067 and will be released in the next release.