Removing a transform track from the sequencer will no longer clean up spawnable actor when the sequencer is closed

Note :
Reopening the level sequence causes ensure failed. (also see callstack)

LogOutputDevice: Error: === Handled ensure: ===
LogOutputDevice: Error: Ensure condition failed: InstanceRegistry->IsHandleValid(InstanceHandle) [File:E:/dev/UnrealEngine-4.26.0/Engine/Source/Runtime/MovieScene/Private/EntitySystem/MovieSceneSpawnablesSystem.cpp] [Line: 174]

The same operation works fine on 4.25. And the licensee wants it to work correctly without a transform track.

1. Create new level sequence
2. Drag and drop an actor blueprint asset into sequencer window to create a actor track as spawnable
3. Make sure the spawnable actor is placed in the world outliner
4. Remove transform track in the actor
5. Close the sequencer window
6. See the world outliner

Result

The spawnable actor remains undeleted

> [Inline Frame] UE4Editor-MovieScene.dll!UMovieSceneSpawnablesSystem::OnRun::_l2::<lambda_f8bbb0465dfb43e73075e6da2c9bd285>:[Image Removed])::l3::<lambda_316140e09360e10f819d0fc4ec28e2a2>::operator()() Line 174 C++ Symbols loaded.> [Inline Frame] UE4Editor-MovieScene.dll!UMovieSceneSpawnablesSystem::OnRun::l2::<lambda_f8bbb0465dfb43e73075e6da2c9bd285>:[Image Removed])::l3::<lambda_316140e09360e10f819d0fc4ec28e2a2>::operator()() Line 174 C++ Symbols loaded.  [Inline Frame] UE4Editor-MovieScene.dll!UMovieSceneSpawnablesSystem::OnRun::l2::<lambda_f8bbb0465dfb43e73075e6da2c9bd285>::operator()(UE::MovieScene::FInstanceHandle InstanceHandle, const FGuid &) Line 174 C++ Symbols loaded.  UE4Editor-MovieScene.dll!UE::MovieScene::TEntityTaskComponentsImpl<TIntegerSequence<int,0,1>,UE::MovieScene::TRead<UE::MovieScene::FInstanceHandle>,UE::MovieScene::TRead<FGuid>>::Iterate_PerEntityImpl<<lambda_f8bbb0465dfb43e73075e6da2c9bd285> &>(UE::MovieScene::FEntityManager * EntityManager, const UE::MovieScene::FEntityComponentFilter & Filter, UMovieSceneSpawnablesSystem::OnRun::l2::<lambda_f8bbb0465dfb43e73075e6da2c9bd285> & InCallback) Line 677 C++ Symbols loaded.  [Inline Frame] UE4Editor-MovieScene.dll!UE::MovieScene::TFilteredEntityTask<UE::MovieScene::TRead<UE::MovieScene::FInstanceHandle>,UE::MovieScene::TRead<FGuid>>::Iterate_PerEntity(UE::MovieScene::FEntityManager * EntityManager, UMovieSceneSpawnablesSystem::OnRun::l2::<lambda_f8bbb0465dfb43e73075e6da2c9bd285> &) Line 1069 C++ Symbols loaded.  UE4Editor-MovieScene.dll!UMovieSceneSpawnablesSystem::OnRun(UE::MovieScene::FSystemTaskPrerequisites & InPrerequisites, UE::MovieScene::FSystemSubsequentTasks & Subsequents) Line 183 C++ Symbols loaded.  UE4Editor-MovieScene.dll!UMovieSceneEntitySystem::Run(UE::MovieScene::FSystemTaskPrerequisites & InPrerequisites, UE::MovieScene::FSystemSubsequentTasks & Subsequents) Line 339 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneEntitySystemGraph::ExecutePhase<TArray<unsigned short,TInlineAllocator<4,TSizedDefaultAllocator<32>>>>(const TArray<unsigned short,TInlineAllocator<4,TSizedDefaultAllocator<32>>> & SortedEntries, UMovieSceneEntitySystemLinker * Linker, TArray<TRefCountPtr<FGraphEvent>,TInlineAllocator<4,TSizedDefaultAllocator<32>>> & OutTasks) Line 716 C++ Symbols loaded.  [Inline Frame] UE4Editor-MovieScene.dll!FMovieSceneEntitySystemGraph::ExecutePhase(UE::MovieScene::ESystemPhase) Line 664 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneEntitySystemRunner::GameThread_SpawnPhase() Line 294 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneEntitySystemRunner::GameThread_ProcessQueue() Line 249 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneEntitySystemRunner::DoFlushUpdateQueueOnce() Line 168 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneEntitySystemRunner::Flush() Line 138 C++ Symbols loaded.  UE4Editor-MovieScene.dll!FMovieSceneRootEvaluationTemplateInstance::Evaluate(FMovieSceneContext Context, IMovieScenePlayer & Player) Line 113 C++ Symbols loaded.  UE4Editor-Sequencer.dll!FSequencer::EvaluateInternal(FMovieSceneEvaluationRange InRange, bool bHasJumped) Line 3100 C++ Symbols loaded.  UE4Editor-Sequencer.dll!FSequencer::Tick(float InDeltaTime) Line 783 C++ Symbols loaded.  UE4Editor-UnrealEd.dll!FTickableEditorObject::TickObjects(const float DeltaSeconds) Line 45 C++ Symbols loaded.  UE4Editor-UnrealEd.dll!UEditorEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 1501 C++ Symbols loaded.  UE4Editor-UnrealEd.dll!UUnrealEdEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 426 C++ Symbols loaded.  UE4Editor.exe!FEngineLoop::Tick() Line 4834 C++ Symbols loaded.  [Inline Frame] UE4Editor.exe!EngineTick() Line 62 C++ Symbols loaded.  UE4Editor.exe!GuardedMain(const wchar_t * CmdLine) Line 169 C++ Symbols loaded.  UE4Editor.exe!GuardedMainWrapper(const wchar_t * CmdLine) Line 137 C++ Symbols loaded.  UE4Editor.exe!WinMain(HINSTANCE_ * hInInstance, HINSTANCE__ * hPrevInstance, char * _formal, int nCmdShow) Line 268 C++ Symbols loaded.  [Inline Frame] UE4Editor.exe!invoke_main() Line 102 C++ Symbols loaded.  UE4Editor.exe!_scrt_common_main_seh() Line 288 C++ Symbols loaded.