Editor Crashing Repeatedly on opening any blueprint after 5.6 upgrade

Development Programming & Scripting Blueprint
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1

Hi,

I upgraded my project from Unreal Engine 5.4 to 5.6.

It compiles in visual studio and editor launches normally.

But the editor crashes every time I try to open any blueprint or a level. Even the newly created empty blueprints crashes.

Using visual studio debugger I managed to find a problematic old blueprint. Its parent C++ class has been deleted.

In 5.4 it warns you of missing parent if you try to open it but not affected if you open other blueprints.

5.6 the warning from 5.4 is not present anymore. It also appears to load unrelated blueprints when you open the editor.

The 5.6 editor also crashes when I try to delete the problematic blueprint.

Is there a setting in 5.6 to stop blueprints getting serialized or compiled automatically?

Thank you,

This is one of the stack traces from crash:

>	[Inline Frame] UnrealEditor-CoreUObject.dll!UClass::Serialize::__l169::<lambda_2>::operator()() Line 6150	C++
 	UnrealEditor-CoreUObject.dll!UClass::Serialize(FArchive & Ar) Line 6150	C++
 	UnrealEditor-Engine.dll!UBlueprintGeneratedClass::Serialize(FArchive & Ar) Line 2579	C++
 	UnrealEditor-CoreUObject.dll!FLinkerLoad::Preload(UObject * Object) Line 4887	C++
 	UnrealEditor-CoreUObject.dll!FLinkerLoad::CreateExport(int Index) Line 5740	C++
 	[Inline Frame] UnrealEditor-CoreUObject.dll!FLinkerLoad::IndexToObject(FPackageIndex) Line 6028	C++
 	[Inline Frame] UnrealEditor-CoreUObject.dll!FLinkerLoad::ResolveResource(FPackageIndex) Line 4566	C++
 	UnrealEditor-CoreUObject.dll!FLinkerLoad::operator<<(UObject * & Object) Line 6283	C++
 	UnrealEditor-Core.dll!FStructuredArchiveSlot::operator<<(UObject * & Value) Line 267	C++
 	UnrealEditor-CoreUObject.dll!FObjectProperty::SerializeItem(FStructuredArchiveSlot Slot, void * Value, const void * Defaults) Line 239	C++
 	UnrealEditor-CoreUObject.dll!FPropertyTag::SerializeTaggedProperty(FStructuredArchiveSlot Slot, FProperty * Property, unsigned char * Value, const unsigned char * Defaults) Line 582	C++
 	UnrealEditor-CoreUObject.dll!UStruct::SerializeVersionedTaggedProperties(FStructuredArchiveSlot Slot, unsigned char * Data, UStruct * DefaultsStruct, unsigned char * Defaults, const UObject * BreakRecursionIfFullyLoad) Line 1928	C++
 	UnrealEditor-CoreUObject.dll!UStruct::SerializeTaggedProperties(FStructuredArchiveSlot Slot, unsigned char * Data, UStruct * DefaultsStruct, unsigned char * Defaults, const UObject * BreakRecursionIfFullyLoad) Line 1507	C++
 	UnrealEditor-CoreUObject.dll!UObject::SerializeScriptProperties(FStructuredArchiveSlot Slot) Line 1977	C++
 	UnrealEditor-CoreUObject.dll!UObject::Serialize(FStructuredArchiveRecord Record) Line 1745	C++
 	UnrealEditor-CoreUObject.dll!UObject::Serialize(FArchive & Ar) Line 1601	C++
 	UnrealEditor-Engine.dll!UBlueprintCore::Serialize(FArchive & Ar) Line 286	C++
 	UnrealEditor-Engine.dll!UBlueprint::Serialize(FArchive & Ar) Line 430	C++
 	UnrealEditor-CoreUObject.dll!FLinkerLoad::Preload(UObject * Object) Line 4887	C++
 	UnrealEditor-CoreUObject.dll!FAsyncPackage2::PreloadLinkerLoadExports(FAsyncLoadingThreadState2 & ThreadState) Line 6865	C++
 	UnrealEditor-CoreUObject.dll!FAsyncPackage2::Event_PreloadLinkerLoadExports(FAsyncLoadingThreadState2 & ThreadState, FAsyncPackage2 * Package, int __formal) Line 7272	C++
 	UnrealEditor-CoreUObject.dll!FEventLoadNode2::Execute(FAsyncLoadingThreadState2 & ThreadState) Line 5713	C++
 	UnrealEditor-CoreUObject.dll!FAsyncLoadEventQueue2::ExecuteSyncLoadEvents(FAsyncLoadingThreadState2 & ThreadState) Line 5920	C++
 	UnrealEditor-CoreUObject.dll!FAsyncLoadingThread2::ProcessAsyncLoadingFromGameThread(FAsyncLoadingThreadState2 & ThreadState, bool & bDidSomething) Line 9215	C++
 	[Inline Frame] UnrealEditor-CoreUObject.dll!FAsyncLoadingThread2::TickAsyncThreadFromGameThread(FAsyncLoadingThreadState2 &) Line 9946	C++
 	UnrealEditor-CoreUObject.dll!FAsyncLoadingThread2::TickAsyncLoadingFromGameThread(FAsyncLoadingThreadState2 & ThreadState, bool bUseTimeLimit, bool bUseFullTimeLimit, double TimeLimit, TArrayView<int const ,int> FlushRequestIDs, bool & bDidSomething) Line 9565	C++
 	UnrealEditor-CoreUObject.dll!FAsyncLoadingThread2::FlushLoading(TArrayView<int const ,int> RequestIDs) Line 11242	C++
 	UnrealEditor-CoreUObject.dll!FlushAsyncLoading(TArrayView<int const ,int> RequestIds) Line 362	C++
 	UnrealEditor-CoreUObject.dll!FlushAsyncLoading(int RequestId) Line 331	C++
 	UnrealEditor-CoreUObject.dll!LoadPackageInternal(UPackage * InOuter, const FPackagePath & PackagePath, unsigned int LoadFlags, FLinkerLoad * ImportLinker, FArchive * InReaderOverride, const FLinkerInstancingContext * InstancingContext, const FPackagePath * DiffPackagePath) Line 1771	C++
 	UnrealEditor-CoreUObject.dll!LoadPackage(UPackage * InOuter, const FPackagePath & PackagePath, unsigned int LoadFlags, FArchive * InReaderOverride, const FLinkerInstancingContext * InstancingContext, const FPackagePath * DiffPackagePath) Line 2135	C++
 	UnrealEditor-CoreUObject.dll!LoadPackage(UPackage * InOuter, const wchar_t * InLongPackageNameOrFilename, unsigned int LoadFlags, FArchive * InReaderOverride, const FLinkerInstancingContext * InstancingContext) Line 2111	C++
 	UnrealEditor-ContentBrowserAssetDataSource.dll!FAssetData::FastGetAsset(bool bLoad, TSet<FName,DefaultKeyFuncs<FName,0>,FDefaultSetAllocator> LoadTags) Line 534	C++
 	[Inline Frame] UnrealEditor-ContentBrowserAssetDataSource.dll!FAssetData::GetAsset(TSet<FName,DefaultKeyFuncs<FName,0>,FDefaultSetAllocator>) Line 567	C++
 	UnrealEditor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditOrPreviewAssetFileItems(TArrayView<TSharedRef<FContentBrowserAssetFileItemDataPayload const ,1> const ,int> InAssetPayloads, EAssetTypeActivationMethod::Type ActivationMethod, const EAssetTypeActivationOpenedMethod OpenedMethod) Line 403	C++
 	UnrealEditor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditOrPreviewItems(IAssetTools * InAssetTools, const UContentBrowserDataSource * InOwnerDataSource, TArrayView<FContentBrowserItemData const ,int> InItems, EAssetTypeActivationMethod::Type ActivationMethod, EAssetTypeActivationOpenedMethod OpenedMethod) Line 459	C++
 	[Inline Frame] UnrealEditor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditItems(IAssetTools *) Line 466	C++
 	UnrealEditor-ContentBrowserAssetDataSource.dll!UContentBrowserAssetDataSource::BulkEditItems(TArrayView<FContentBrowserItemData const ,int> InItems) Line 2663	C++
 	UnrealEditor-ContentBrowser.dll!SContentBrowser::OnItemsActivated(TArrayView<FContentBrowserItem const ,int> ActivatedItems, EAssetTypeActivationMethod::Type ActivationMethod) Line 3193	C++
 	[Inline Frame] UnrealEditor-ContentBrowser.dll!Invoke(void(SContentBrowser::*)(TArrayView<FContentBrowserItem const ,int>, EAssetTypeActivationMethod::Type)) Line 66	C++
 	[Inline Frame] UnrealEditor-ContentBrowser.dll!UE::Core::Private::Tuple::TTupleBase<TIntegerSequence<unsigned int>>::ApplyAfter(void(SContentBrowser::*)(TArrayView<FContentBrowserItem const ,int>, EAssetTypeActivationMethod::Type) &) Line 320	C++
 	UnrealEditor-ContentBrowser.dll!V::TBaseSPMethodDelegateInstance::Execute(TArrayView<FContentBrowserItem const ,int> <Params_0>, EAssetTypeActivationMethod::Type <Params_1>) Line 292	C++
 	[Inline Frame] UnrealEditor-ContentBrowser.dll!TDelegate<void __cdecl(TArrayView<FContentBrowserItem const ,int>,enum EAssetTypeActivationMethod::Type),FDefaultDelegateUserPolicy>::Execute(TArrayView<FContentBrowserItem const ,int>) Line 614	C++
 	UnrealEditor-ContentBrowser.dll!SAssetView::OnListMouseButtonDoubleClick(TSharedPtr<FAssetViewItem,1> AssetItem) Line 5525	C++
 	[Inline Frame] UnrealEditor-ContentBrowser.dll!Invoke(void(SAssetView::*)(TSharedPtr<FAssetViewItem,1>)) Line 66	C++
 	[Inline Frame] UnrealEditor-ContentBrowser.dll!UE::Core::Private::Tuple::TTupleBase<TIntegerSequence<unsigned int>>::ApplyAfter(void(SAssetView::*)(TSharedPtr<FAssetViewItem,1>) &) Line 320	C++
 	UnrealEditor-ContentBrowser.dll!V::TBaseSPMethodDelegateInstance::ExecuteIfSafe(TSharedPtr<FAssetViewItem,1> <Params_0>) Line 309	C++
 	UnrealEditor-ContentBrowser.dll!TDelegate<void __cdecl(TSharedPtr<FAssetViewItem,1>),FDefaultDelegateUserPolicy>::ExecuteIfBound<void,0>(TSharedPtr<FAssetViewItem,1> <Params_0>) Line 635	C++
 	UnrealEditor-ContentBrowser.dll!SListView<TSharedPtr<FAssetViewItem,1>>::Private_OnItemDoubleClicked(TSharedPtr<FAssetViewItem,1> TheItem) Line 1154	C++
 	UnrealEditor-ContentBrowser.dll!STableRow<TSharedPtr<FAssetViewItem,1>>::OnMouseButtonDoubleClick(const FGeometry & InMyGeometry, const FPointerEvent & InMouseEvent) Line 438	C++
 	[Inline Frame] UnrealEditor-Slate.dll!FSlateApplication::RoutePointerDoubleClickEvent::__l2::<lambda_1>::operator()(const FArrangedWidget &) Line 5856	C++
 	UnrealEditor-Slate.dll!??$Route@VFReply@@VFBubblePolicy@FEventRouter@@UFPointerEvent@@V<lambda_1>@?1??RoutePointerDoubleClickEvent@FSlateApplication@@QEAA?AV1@AEBVFWidgetPath@@AEBU4@@Z@@FEventRouter@@SA?AVFReply@@PEAVFSlateApplication@@VFBubblePolicy@0@UFPointerEvent@@AEBV<lambda_1>@?1??RoutePointerDoubleClickEvent@2@QEAA?AV1@AEBVFWidgetPath@@AEBU4@@Z@W4ESlateDebuggingInputEvent@@@Z(FSlateApplication * ThisApplication, FEventRouter::FBubblePolicy RoutingPolicy, FPointerEvent EventCopy, const FSlateApplication::RoutePointerDoubleClickEvent::__l2::<lambda_1> & Lambda, ESlateDebuggingInputEvent DebuggingInputEvent) Line 456	C++
 	UnrealEditor-Slate.dll!FSlateApplication::RoutePointerDoubleClickEvent(const FWidgetPath & WidgetsUnderPointer, const FPointerEvent & PointerEvent) Line 5854	C++
 	UnrealEditor-Slate.dll!FSlateApplication::ProcessMouseButtonDoubleClickEvent(const TSharedPtr<FGenericWindow,1> & PlatformWindow, const FPointerEvent & InMouseEvent) Line 5839	C++
 	UnrealEditor-Slate.dll!FSlateApplication::OnMouseDoubleClick(const TSharedPtr<FGenericWindow,1> & PlatformWindow, const EMouseButtons::Type Button, const UE::Math::TVector2<double> CursorPos) Line 5802	C++
 	UnrealEditor-ApplicationCore.dll!FWindowsApplication::ProcessDeferredMessage(const FDeferredWindowsMessage & DeferredMessage) Line 3056	C++
 	UnrealEditor-ApplicationCore.dll!FWindowsApplication::DeferMessage(TSharedPtr<FWindowsWindow,1> & NativeWindow, HWND__ * InHWnd, unsigned int InMessage, unsigned __int64 InWParam, __int64 InLParam, int MouseX, int MouseY, unsigned int RawInputFlags) Line 3570	C++
 	UnrealEditor-ApplicationCore.dll!FWindowsApplication::ProcessMessage(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 2725	C++
 	[Inline Frame] UnrealEditor-ApplicationCore.dll!WindowsApplication_WndProc(HWND__ *) Line 1716	C++
 	UnrealEditor-ApplicationCore.dll!FWindowsApplication::AppWndProc(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 1722	C++
 	[External Code]	
 	[Inline Frame] UnrealEditor-ApplicationCore.dll!WinPumpMessages() Line 116	C++
 	UnrealEditor-ApplicationCore.dll!FWindowsPlatformApplicationMisc::PumpMessages(bool bFromMainLoop) Line 145	C++
 	UnrealEditor.exe!FEngineLoop::Tick() Line 5554	C++
 	[Inline Frame] UnrealEditor.exe!EngineTick() Line 60	C++
 	UnrealEditor.exe!GuardedMain(const wchar_t * CmdLine) Line 187	C++
 	UnrealEditor.exe!GuardedMainWrapper(const wchar_t * CmdLine) Line 128	C++
 	UnrealEditor.exe!LaunchWindowsStartup(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow, const wchar_t * CmdLine) Line 282	C++
 	UnrealEditor.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * pCmdLine, int nCmdShow) Line 339	C++
 	[External Code]
2

Hello there @asbe!

Checking with my peers, and looking through your trace, the conflict seems to arise when the engine tries to access UBlueprintGeneratedClass, then fails to find the reference, either due an outdated registry, or as you mentioned, the fact that the parent class is not there anymore. And this is most likely due the version migration.

Blueprint validation is a bit more strict in 5.6, takes place earlier in the pipeline. And if said blueprint is missing it’s parent, it can bring the whole thing down. Before, in 5.4, this was just a warning.

So, the best approach here would be to give the engine what it wants. You can recreate the missing class as a dummy, with the exact name as the deleted parent. It won’t need logic, just to exist. Then you can recompile, and the blueprint will have it’s parent again. At this point, you should be able to load the blueprint without crashing, and safely delete the whole thing.

If that doesn’t work, then the other path would be to clear up your cache, and get rid of all the old references, including the missing parent. To do so, close both UE and VS, go to your project’s main directory, and delete the following folders from there:

  • Binaries/
  • Intermediate/
  • DerivedDataCache/
  • Saved/

After that, go to your Content folder, and manually delete the .uasset file tied to the conflicting blueprint. Now you can right click on your .uproject file, and pick “Generate Visual Studio project files”. Finally, recompile and reopen your project.

Hope this helps, and good luck!