Infinite hang when reloading a scene contains a manually spawned NetworkObject with a SpriteLibrary and a SpriteResolver

Description

Infinite hang when reloading a scene contains a manually spawned NetworkObject with a SpriteLibrary and a SpriteResolver

Reproduce Steps

1. Create an empty scene
2. Add a NetworkManager, with UnityTransport
3. Create a new prefab with NetworkObject, SpriteRenderer, Animator, SpriteLibrary, SpriteResolver (following basically this tutorial: https://www.youtube.com/watch?v=4xPHqEEa-V0)
4. Create an empty object TestCrash with the following code, and link the prefab from (3) in the inspector

public class TestCrash : NetworkBehaviour
{
    [SerializeField] public GameObject prefab = null!;
    private bool _alreadyCalled;

    private void Start()
    {
        var networkManager = NetworkManager.Singleton;
        var unityTransport = networkManager.GetComponent<UnityTransport>();

        // Start local server
        unityTransport.UseWebSockets = false; // if applicable
        unityTransport.SetConnectionData("0.0.0.0", 7777);
        networkManager!.NetworkConfig.NetworkTransport = unityTransport;
        networkManager.StartHost();

        NetworkManager.Singleton.SpawnManager.InstantiateAndSpawn(
            prefab!.GetComponent<NetworkObject>(),
            OwnerClientId,
            destroyWithScene: true,
            position: Vector3.zero
        );
    }

    private void Update()
    {
        if (_alreadyCalled) return;
        if (Time.timeSinceLevelLoad < 3f) return;
        _alreadyCalled = true;
       NetworkManager.Singleton.SceneManager.LoadScene(SceneManager.GetActiveScene().name, LoadSceneMode.Single);
    }
}

TestCrash is some code that

• starts a local server
• spawns the prefab
• waits 3 seconds
• reloads the scene

Actual Outcome

After a few attempts, the scene never reloads and the Unity editor hangs forever (has to be force quitted)

Expected Outcome

The scene reloads every 3s

Environment

• OS: Windows 11
• Unity Version: 6000.4.7f1
• Netcode Version: 2.12.0

Additional Context

• This bug did not happen with 2.12.0 and Unity 6000.3.11f1 (started happening after upgrading to 6000.4.7f1)
• The bug doesn't happen without destroyWithScene: true,
• Removing the SpriteResolver/SpriteLibrary stops the bug from happening
• The NetworkObject must be spawned with InstantiateAndSpawn, if the prefab is added to the scene, the bug doesn't happen

Here is a dump of the Main Thread stack when the editor is hanging. The CPU is at 0% at that point. Maybe a lock contention?

<unknown> 0x00007ff973d63cb4
<unknown> 0x00007ff973c30543
<unknown> 0x00007ff97107e558
UnityClassic::Baselib_SystemFutex_Wait(int * __ptr64,int,unsigned int) 0x00007ff8886af7f6
ProfilerMutexLock(Mutex & __ptr64,char const * __ptr64,profiling::Marker & __ptr64,char const * __ptr64,int) 0x00007ff88b1a4450
PersistentManager::Lock(PersistentManager::LockFlags,profiling::Marker * __ptr64) __ptr64 0x00007ff88b1a1b83
PersistentManager::GetPathName(EntityId) __ptr64 0x00007ff88b1968bb
GetGUIDFromEntityId(EntityId) 0x00007ff888e786fe
AssetChangedNotifier::UnsubscribeFromAll(EntityId) __ptr64 0x00007ff88a209aee
SpriteRenderer::MainThreadCleanup(void) __ptr64 0x00007ff88b631e42
delete_object_internal_step1(Object * __ptr64) 0x00007ff88b8cd380
CommitBatchDelete(BatchDelete & __ptr64) 0x00007ff88b5286d2
DestroyObjectHighLevel_Internal(Object * __ptr64,bool) 0x00007ff88b532e31
DestroyObjectHighLevel(Object * __ptr64,bool) 0x00007ff88b532ba8
DelayedDestroyCallback(Object * __ptr64,void * __ptr64) 0x00007ff88b7963cb
DelayedCallManager::Update(int) __ptr64 0x00007ff88b797ac8
<unknown> 0x00007ff88b4f9d6b
ExecutePlayerLoop(NativePlayerLoopSystem * __ptr64) 0x00007ff88b517f5b
ExecutePlayerLoop(NativePlayerLoopSystem * __ptr64) 0x00007ff88b51811a
PlayerLoop(void) 0x00007ff88b51d105
EditorPlayerLoop::Execute(void) __ptr64 0x00007ff889ab957a
PlayerLoopController::InternalUpdateScene(bool,bool) __ptr64 0x00007ff889ab2a9c
PlayerLoopController::UpdateSceneIfNeededFromMainLoop(void) __ptr64 0x00007ff889ab4dad
Application::TickTimer(void) __ptr64 0x00007ff889acc4c3
<unknown> 0x00007ff8894bfb2c
UnityMain 0x00007ff8894c8693
<unknown> 0x00007ff6ae972f2a
<unknown> 0x00007ff97360e957
<unknown> 0x00007ff973caad6c

Comece reproduzindo a configuração com NetworkManager, UnityTransport, InstantiateAndSpawn, SpriteLibrary, SpriteResolver e destroyWithScene habilitados e, em seguida, rastreie NetworkManager.SceneManager.LoadScene durante recarregamentos repetidos. Compare o comportamento entre as versões relatadas do Unity e do Netcode; considera-se concluído quando a cena recarregar a cada 3 segundos sem que o editor do Unity trave.