Steps to Reproduce

Download the licensee repro here - [Link Removed]

Open in 4.27, attempt to open MI_UI_MC_Ceiling_pillar_8x8_01a, it will crash.

Callstack
Assertion failed: !ParentLayerIndices.Contains(ParentLayerIndex) [File:D:/Unreal/UE4_Release-4.27/Engine/Source/Runtime/Engine/Private/Materials/MaterialExpressions.cpp] [Line: 13167] UE4Editor.exe has triggered a breakpoint.
>	UE4Editor-Engine.dll!FMaterialLayersFunctions::ResolveParent(const FMaterialLayersFunctions & Parent, TArray<int,TSizedDefaultAllocator<32>> & OutRemapLayerIndices) Line 13167	C++
 	UE4Editor-Engine.dll!UMaterialInstance::UpdateParameters() Line 601	C++
 	UE4Editor-Engine.dll!UMaterialInstance::UpdateParameterNames() Line 4013	C++
 	UE4Editor-UnrealEd.dll!UMaterialEditorInstanceConstant::RegenerateArrays() Line 1164	C++
 	UE4Editor-UnrealEd.dll!UMaterialEditorInstanceConstant::SetSourceInstance(UMaterialInstanceConstant * MaterialInterface) Line 1753	C++
 	UE4Editor-MaterialEditor.dll!FMaterialInstanceEditor::InitMaterialInstanceEditor(const EToolkitMode::Type Mode, const TSharedPtr<IToolkitHost,0> & InitToolkitHost, UObject * ObjectToEdit) Line 376	C++
 	UE4Editor-MaterialEditor.dll!FMaterialEditorModule::CreateMaterialInstanceEditor(const EToolkitMode::Type Mode, const TSharedPtr<IToolkitHost,0> & InitToolkitHost, UMaterialInstance * MaterialInstance) Line 105	C++
 	UE4Editor-AssetTools.dll!FAssetTypeActions_MaterialInstanceConstant::OpenAssetEditor(const TArray<UObject *,TSizedDefaultAllocator<32>> & InObjects, TSharedPtr<IToolkitHost,0> EditWithinLevelEditor) Line 39	C++
 	UE4Editor-UnrealEd.dll!UAssetEditorSubsystem::OpenEditorForAsset(UObject * Asset, const EToolkitMode::Type ToolkitMode, TSharedPtr<IToolkitHost,0> OpenedFromLevelEditor, const bool bShowProgressWindow) Line 363	C++
 	UE4Editor-UnrealEd.dll!UAssetEditorSubsystem::OpenEditorForAssets_Advanced(const TArray<UObject *,TSizedDefaultAllocator<32>> & InAssets, const EToolkitMode::Type ToolkitMode, TSharedPtr<IToolkitHost,0> OpenedFromLevelEditor) Line 437	C++
 	UE4Editor-UnrealEd.dll!UAssetEditorSubsystem::OpenEditorForAssets(const TArray<UObject *,TSizedDefaultAllocator<32>> & Assets) Line 553	C++
 	UE4Editor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditOrPreviewAssetFileItems(TArrayView<TSharedRef<FContentBrowserAssetFileItemDataPayload const ,0> const ,int> InAssetPayloads, const bool bIsPreview) Line 298	C++
 	UE4Editor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditOrPreviewItems(IAssetTools * InAssetTools, const UContentBrowserDataSource * InOwnerDataSource, TArrayView<FContentBrowserItemData const ,int> InItems, const bool bIsPreview) Line 318	C++
 	[Inline Frame] UE4Editor-ContentBrowserAssetDataSource.dll!ContentBrowserAssetData::EditItems(IAssetTools * InAssetTools, const UContentBrowserDataSource *) Line 323	C++
 	UE4Editor-ContentBrowserAssetDataSource.dll!UContentBrowserAssetDataSource::BulkEditItems(TArrayView<FContentBrowserItemData const ,int> InItems) Line 1030	C++
 	UE4Editor-ContentBrowser.dll!SContentBrowser::OnItemsActivated(TArrayView<FContentBrowserItem const ,int> ActivatedItems, EAssetTypeActivationMethod::Type ActivationMethod) Line 2281	C++
 	[Inline Frame] UE4Editor-ContentBrowser.dll!Invoke(void(SContentBrowser::*)(TArrayView<FContentBrowserItem const ,int>, EAssetTypeActivationMethod::Type)) Line 65	C++
 	[Inline Frame] UE4Editor-ContentBrowser.dll!UE4Tuple_Private::TTupleBase<TIntegerSequence<unsigned int>>::ApplyAfter(void(SContentBrowser::*)(TArrayView<FContentBrowserItem const ,int>, EAssetTypeActivationMethod::Type) &) Line 306	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,void __cdecl(TArrayView<FContentBrowserItem const ,int>,enum EAssetTypeActivationMethod::Type),FDefaultDelegateUserPolicy>::Execute(TArrayView<FContentBrowserItem const ,int> <Params_0>, EAssetTypeActivationMethod::Type <Params_1>) Line 290	C++
 	[Inline Frame] UE4Editor-ContentBrowser.dll!TDelegate<void __cdecl(TArrayView<FContentBrowserItem const ,int>,enum EAssetTypeActivationMethod::Type),FDefaultDelegateUserPolicy>::Execute(TArrayView<FContentBrowserItem const ,int>) Line 580	C++
 	UE4Editor-ContentBrowser.dll!SAssetView::OnListMouseButtonDoubleClick(TSharedPtr<FAssetViewItem,0> AssetItem) Line 3548	C++
 	[Inline Frame] UE4Editor-ContentBrowser.dll!Invoke(void(SAssetView::*)(TSharedPtr<FAssetViewItem,0>)) Line 65	C++
 	[Inline Frame] UE4Editor-ContentBrowser.dll!UE4Tuple_Private::TTupleBase<TIntegerSequence<unsigned int>>::ApplyAfter(void(SAssetView::*)(TSharedPtr<FAssetViewItem,0>) &) Line 306	C++
 	UE4Editor-ContentBrowser.dll!TBaseSPMethodDelegateInstance<0,SAssetView,0,void __cdecl(TSharedPtr<FAssetViewItem,0>),FDefaultDelegateUserPolicy>::ExecuteIfSafe(TSharedPtr<FAssetViewItem,0> <Params_0>) Line 307	C++
 	UE4Editor-ContentBrowser.dll!TDelegate<void __cdecl(TSharedPtr<FAssetViewItem,0>),FDefaultDelegateUserPolicy>::ExecuteIfBound<void,0>(TSharedPtr<FAssetViewItem,0> <Params_0>) Line 599	C++
 	UE4Editor-ContentBrowser.dll!SListView<TSharedPtr<FAssetViewItem,0>>::Private_OnItemDoubleClicked(TSharedPtr<FAssetViewItem,0> TheItem) Line 1074	C++
 	UE4Editor-ContentBrowser.dll!STableRow<TSharedPtr<FAssetViewItem,0>>::OnMouseButtonDoubleClick(const FGeometry & InMyGeometry, const FPointerEvent & InMouseEvent) Line 461	C++
 	[Inline Frame] UE4Editor-Slate.dll!FSlateApplication::RoutePointerDoubleClickEvent::__l2::<lambda_2b5148752c2a272000c47b69ff14a42e>::operator()(const FArrangedWidget &) Line 5299	C++
 	UE4Editor-Slate.dll!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FPointerEvent,<lambda_2b5148752c2a272000c47b69ff14a42e>>(FSlateApplication * ThisApplication, FEventRouter::FBubblePolicy RoutingPolicy, FPointerEvent EventCopy, const FSlateApplication::RoutePointerDoubleClickEvent::__l2::<lambda_2b5148752c2a272000c47b69ff14a42e> & Lambda, ESlateDebuggingInputEvent DebuggingInputEvent) Line 378	C++
 	UE4Editor-Slate.dll!FSlateApplication::RoutePointerDoubleClickEvent(const FWidgetPath & WidgetsUnderPointer, const FPointerEvent & PointerEvent) Line 5297	C++
 	UE4Editor-Slate.dll!FSlateApplication::ProcessMouseButtonDoubleClickEvent(const TSharedPtr<FGenericWindow,0> & PlatformWindow, const FPointerEvent & InMouseEvent) Line 5284	C++
 	UE4Editor-Slate.dll!FSlateApplication::OnMouseDoubleClick(const TSharedPtr<FGenericWindow,0> & PlatformWindow, const EMouseButtons::Type Button, const FVector2D CursorPos) Line 5247	C++
 	UE4Editor-ApplicationCore.dll!FWindowsApplication::ProcessDeferredMessage(const FDeferredWindowsMessage & DeferredMessage) Line 2209	C++
 	UE4Editor-ApplicationCore.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 2698	C++
 	UE4Editor-ApplicationCore.dll!FWindowsApplication::ProcessMessage(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 1881	C++
 	[Inline Frame] UE4Editor-ApplicationCore.dll!WindowsApplication_WndProc(HWND__ *) Line 899	C++
 	UE4Editor-ApplicationCore.dll!FWindowsApplication::AppWndProc(HWND__ * hwnd, unsigned int msg, unsigned __int64 wParam, __int64 lParam) Line 905	C++
 	user32.dll!UserCallWinProcCheckWow()	Unknown
 	user32.dll!DispatchMessageWorker()	Unknown
 	[Inline Frame] UE4Editor-ApplicationCore.dll!WinPumpMessages() Line 103	C++
 	UE4Editor-ApplicationCore.dll!FWindowsPlatformApplicationMisc::PumpMessages(bool bFromMainLoop) Line 125	C++
 	UE4Editor.exe!FEngineLoop::Tick() Line 4848	C++
 	[Inline Frame] UE4Editor.exe!EngineTick() Line 62	C++
 	UE4Editor.exe!GuardedMain(const wchar_t * CmdLine) Line 178	C++
 	UE4Editor.exe!LaunchWindowsStartup(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow, const wchar_t * CmdLine) Line 262	C++
 	UE4Editor.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * pCmdLine, int nCmdShow) Line 320	C++
 	[Inline Frame] UE4Editor.exe!invoke_main() Line 102	C++
 	UE4Editor.exe!__scrt_common_main_seh() Line 288	C++
 	kernel32.dll!BaseThreadInitThunk()	Unknown
 	ntdll.dll!RtlUserThreadStart()	Unknown

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Fixed
ComponentRendering
Affects Versions4.27
Target Fix4.27
Fix Commit16493398
Main Commit16493407
Release Commit16493398
CreatedMay 26, 2021
ResolvedMay 27, 2021
UpdatedJun 7, 2021