- I created a blank 4.8 git c++ project, dev editor, win64.
 
- Created two empty levels (A and B) with only the default ground/box.
 
- In MapA i put MapB as a sublevel with the worldcomposer enabled. (MapB was automatic added because of the composer)
 
- Save all stuff and you need to have MapA opened with MapB loaded! You should see both maps in the viewport.
 
- I try to open MapB from the content browser.
 
It crashes. (it only crashes with composer enabled, if its not enabled it doesnt crash)
I think the problem is that the engine wants to load MapB (as a persistent level), but because of the composer its already loaded as a sublevel inside MapA and this causes the crash.
Call Stack:
>	UE4Editor-UnrealEd.dll!UEditorEngine::CheckForWorldGCLeaks(UWorld * NewWorld, UPackage * WorldPackage) Line 1742	C++
 	UE4Editor-UnrealEd.dll!UEditorEngine::EditorDestroyWorld(FWorldContext & Context, const FText & CleanseText, UWorld * NewWorld) Line 1863	C++
 	UE4Editor-UnrealEd.dll!UEditorEngine::Map_Load(const wchar_t * Str, FOutputDevice & Ar) Line 2213	C++
 	UE4Editor-UnrealEd.dll!UEditorEngine::HandleMapCommand(const wchar_t * Str, FOutputDevice & Ar, UWorld * InWorld) Line 5768	C++
 	UE4Editor-UnrealEd.dll!UEditorEngine::Exec(UWorld * InWorld, const wchar_t * Stream, FOutputDevice & Ar) Line 5262	C++
 	UE4Editor-UnrealEd.dll!UUnrealEdEngine::Exec(UWorld * InWorld, const wchar_t * Stream, FOutputDevice & Ar) Line 742	C++
 	UE4Editor-UnrealEd.dll!FEditorFileUtils::LoadMap(const FString & InFilename, bool LoadAsTemplate, const bool bShowProgress) Line 1987	C++
 	UE4Editor-AssetTools.dll!FAssetTypeActions_World::OpenAssetEditor(const TArray<UObject *,FDefaultAllocator> & InObjects, TSharedPtr<IToolkitHost,0> EditWithinLevelEditor) Line 23	C++
 	UE4Editor-UnrealEd.dll!FAssetEditorManager::OpenEditorForAsset(UObject * Asset, const EToolkitMode::Type ToolkitMode, TSharedPtr<IToolkitHost,0> OpenedFromLevelEditor) Line 303	C++
 	UE4Editor-AssetTools.dll!FAssetTypeActions_Base::AssetsActivated(const TArray<UObject *,FDefaultAllocator> & InObjects, EAssetTypeActivationMethod::Type ActivationType) Line 37	C++
 	UE4Editor-ContentBrowser.dll!SContentBrowser::OnAssetsActivated(const TArray<FAssetData,FDefaultAllocator> & ActivatedAssets, EAssetTypeActivationMethod::Type ActivationMethod) Line 1603	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,TTypeWrapper<void> __cdecl(TArray<FAssetData,FDefaultAllocator> const & __ptr64,enum EAssetTypeActivationMethod::Type)>::Execute(const TArray<FAssetData,FDefaultAllocator> & <Params_0>, EAssetTypeActivationMethod::Type <Params_1>) Line 282	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,void __cdecl(TArray<FAssetData,FDefaultAllocator> const & __ptr64,enum EAssetTypeActivationMethod::Type)>::ExecuteIfSafe(const TArray<FAssetData,FDefaultAllocator> & <Params_0>, EAssetTypeActivationMethod::Type <Params_1>) Line 388	C++
 	UE4Editor-ContentBrowser.dll!SAssetView::OnListMouseButtonDoubleClick(TSharedPtr<FAssetViewItem,0> AssetItem) Line 3222	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SAssetView,0,TTypeWrapper<void> __cdecl(TSharedPtr<FAssetViewItem,0>)>::Execute(TSharedPtr<FAssetViewItem,0> <Params_0>) Line 282	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SAssetView,0,void __cdecl(TSharedPtr<FAssetViewItem,0>)>::ExecuteIfSafe(TSharedPtr<FAssetViewItem,0> <Params_0>) Line 388	C++
 	UE4Editor-ContentBrowser.dll!TBaseDelegate<void,TSharedPtr<FAssetViewItem,0> >::ExecuteIfBound(TSharedPtr<FAssetViewItem,0> <Params_0>) Line 519	C++
 	UE4Editor-ContentBrowser.dll!SListView<TSharedPtr<FAssetViewItem,0> >::Private_OnItemDoubleClicked(TSharedPtr<FAssetViewItem,0> TheItem) Line 689	C++
 	UE4Editor-ContentBrowser.dll!STableRow<TSharedPtr<FAssetViewItem,0> >::OnMouseButtonDoubleClick(const FGeometry & InMyGeometry, const FPointerEvent & InMouseEvent) Line 252	C++
 	UE4Editor-Slate.dll!FSlateApplication::ProcessMouseButtonDoubleClickEvent::__l3::<lambda>(const FArrangedWidget & TargetWidget, const FPointerEvent & Event) Line 4100	C++
 	UE4Editor-Slate.dll!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FPointerEvent,FReply <lambda>(const FArrangedWidget &, const FPointerEvent &) >(FSlateApplication * ThisApplication, FEventRouter::FBubblePolicy RoutingPolicy, FPointerEvent EventCopy, const FSlateApplication::ProcessMouseButtonDoubleClickEvent::__l3::FReply <lambda>(const FArrangedWidget &, const FPointerEvent &) & Lambda) Line 212	C++
 	UE4Editor-Slate.dll!FSlateApplication::ProcessMouseButtonDoubleClickEvent(const TSharedPtr<FGenericWindow,0> & PlatformWindow, FPointerEvent & InMouseEvent) Line 4101	C++
 	UE4Editor-Slate.dll!FSlateApplication::OnMouseDoubleClick(const TSharedPtr<FGenericWindow,0> & PlatformWindow, const EMouseButtons::Type Button) Line 4081	C++
 	UE4Editor-Core.dll!FWindowsApplication::ProcessDeferredMessage(const FDeferredWindowsMessage & DeferredMessage) Line 1348	C++
 	UE4Editor-Core.dll!FWindowsApplication::DeferMessage(TSharedPtr<FWindowsWindow,0> & NativeWindow, HWND__ * InHWnd, unsigned int InMessage, unsigned __int64 InWParam, __int64 InLParam, int MouseX, int MouseY, unsigned int RawInputFlags) Line 1711	C++
 	UE4Editor-Core.dll!FWindowsApplication::ProcessMessage(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 706	C++
 	UE4Editor-Core.dll!FWindowsApplication::AppWndProc(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 628	C++
 	[External Code]	
 	UE4Editor-Core.dll!FWindowsPlatformMisc::PumpMessages(bool bFromMainLoop) Line 792	C++
 	UE4Editor.exe!FEngineLoop::Tick() Line 2319	C++
 	UE4Editor.exe!GuardedMain(const wchar_t * CmdLine, HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, int nCmdShow) Line 142	C++
 	UE4Editor.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow) Line 238	C++
 	[External Code]	
Autos:
+		*RemainingWorld	(Name=0x00000091f22f14b8 "MapA")	UWorld
+		ErrorString	L"   (Object is not currently rooted)\r\n"	FString
		Fatal	Fatal (1)	ELogVerbosity::Type
+		LogEditorServer	{...}	FLogCategoryLogEditorServer
+		RemainingWorld	0x00000091ef288100 (Name=0x00000091f22f14b8 "MapA")	UWorld *
+		Route	Empty	TMap<UObject *,UProperty *,FDefaultSetAllocator,TDefaultMapKeyFuncs<UObject *,UProperty *,0> >
+		TempFname	0x00007ffe8d28c300 L"../../../../../Eigene Dateien/Documents/Unreal Projects/CrashTest/Content/MapB.umap"	wchar_t[512]
+		this	0x00000091e2902b00 (Name=0x00000091d0da9638 "UnrealEdEngine"_0)	UEditorEngine *