Potential workaround for this issue as suggested by a licensee: Window -> Load Layout -> Default Editor Layout
We have been unable to get an internal repro so far, however we have had quite a few reports from the community reporting this issue.
One user also stated this happens when migrating a project over from 4.25, however we were still unable to reproduce that.
Error Message:
Assertion failed: IsValid() [File:D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Public\Templates/SharedPointer.h] [Line: 824]
ntdll!7ff893670000 + 9c034 KERNELBASE!7ff8910e0000 + 1a34e UE4Editor-Core!ReportCrash(_EXCEPTION_POINTERS *) [WindowsPlatformCrashContext.cpp:1574] UE4Editor!7ff6d49d0000 + 3b0ff VCRUNTIME140!7ff876f90000 + e360 ntdll!7ff893670000 + a130f ntdll!7ff893670000 + 4b5e4 ntdll!7ff893670000 + 4b335 KERNELBASE!7ff8910e0000 + 2d759 UE4Editor-Core!ReportAssert(wchar_t const *,int) [WindowsPlatformCrashContext.cpp:1627] UE4Editor-Core!FWindowsErrorOutputDevice::Serialize(wchar_t const *,ELogVerbosity::Type,FName const &) [WindowsErrorOutputDevice.cpp:78] UE4Editor-Core!FOutputDevice::LogfImpl(wchar_t const *,...) [OutputDevice.cpp:61] UE4Editor-Core!static void AssertFailedImplV(const char *, const char *, int, const wchar_t *, char *) [AssertionMacros.cpp:102] UE4Editor-Core!FDebug::CheckVerifyFailedImpl(char const *,char const *,int,wchar_t const *,...) [AssertionMacros.cpp:458] UE4Editor-StaticMeshEditor!FStaticMeshEditor::SpawnTab_PreviewSceneSettings(FSpawnTabArgs const &) [StaticMeshEditor.cpp:537] UE4Editor-StaticMeshEditor!class TSharedRef<SDockTab,0> TBaseSPMethodDelegateInstance<0,FStaticMeshEditor,0,TSharedRef<SDockTab,0> __cdecl(FSpawnTabArgs const &) [DelegateInstancesImpl.h:290] UE4Editor-Slate!FTabManager::SpawnTab(FTabId const &,TSharedPtr<SWindow,0> const &,bool) [TabManager.cpp:1708] UE4Editor-Slate!FTabManager::RestoreArea_Helper(TSharedRef<FTabManager::FLayoutNode,0> const &,TSharedPtr<SWindow,0> const &,bool,EOutputCanBeNullptr) [TabManager.cpp:1445] UE4Editor-Slate!FTabManager::RestoreSplitterContent(TSharedRef<FTabManager::FSplitter,0> const &,TSharedRef<SDockingSplitter,0> const &,TSharedPtr<SWindow,0> const &) [TabManager.cpp:1637] UE4Editor-Slate!FTabManager::RestoreArea_Helper(TSharedRef<FTabManager::FLayoutNode,0> const &,TSharedPtr<SWindow,0> const &,bool,EOutputCanBeNullptr) [TabManager.cpp:1576] UE4Editor-Slate!FTabManager::RestoreSplitterContent(TSharedRef<FTabManager::FSplitter,0> const &,TSharedRef<SDockingSplitter,0> const &,TSharedPtr<SWindow,0> const &) [TabManager.cpp:1637] UE4Editor-Slate!FTabManager::RestoreArea_Helper(TSharedRef<FTabManager::FLayoutNode,0> const &,TSharedPtr<SWindow,0> const &,bool,EOutputCanBeNullptr) [TabManager.cpp:1555] UE4Editor-Slate!FTabManager::RestoreArea(TSharedRef<FTabManager::FArea,0> const &,TSharedPtr<SWindow,0> const &,bool,EOutputCanBeNullptr) [TabManager.cpp:1382] UE4Editor-Slate!FTabManager::RestoreFrom(TSharedRef<FTabManager::FLayout,0> const &,TSharedPtr<SWindow,0> const &,bool,EOutputCanBeNullptr) [TabManager.cpp:865] UE4Editor-UnrealEd!SStandaloneAssetEditorToolkitHost::RestoreFromLayout(TSharedRef<FTabManager::FLayout,0> const &) [SStandaloneAssetEditorToolkitHost.cpp:135] UE4Editor-UnrealEd!SStandaloneAssetEditorToolkitHost::SetupInitialContent(TSharedRef<FTabManager::FLayout,0> const &,TSharedPtr<SDockTab,0> const &,bool) [SStandaloneAssetEditorToolkitHost.cpp:62] UE4Editor-UnrealEd!FAssetEditorToolkit::InitAssetEditor(EToolkitMode::Type,TSharedPtr<IToolkitHost,0> const &,FName,TSharedRef<FTabManager::FLayout,0> const &,bool,bool,TArray<UObject *,TSizedDefaultAllocator<32> > const &,bool,bool) [AssetEditorToolkit.cpp:271] UE4Editor-UnrealEd!FAssetEditorToolkit::InitAssetEditor(EToolkitMode::Type,TSharedPtr<IToolkitHost,0> const &,FName,TSharedRef<FTabManager::FLayout,0> const &,bool,bool,UObject *,bool,bool) [AssetEditorToolkit.cpp:60] UE4Editor-StaticMeshEditor!FStaticMeshEditor::InitStaticMeshEditor(EToolkitMode::Type,TSharedPtr<IToolkitHost,0> const &,UStaticMesh *) [StaticMeshEditor.cpp:267] UE4Editor-StaticMeshEditor!FStaticMeshEditorModule::CreateStaticMeshEditor(EToolkitMode::Type,TSharedPtr<IToolkitHost,0> const &,UStaticMesh *) [StaticMeshEditorModule.cpp:51] UE4Editor-AssetTools!FAssetTypeActions_StaticMesh::OpenAssetEditor(TArray<UObject *,TSizedDefaultAllocator<32> > const &,TSharedPtr<IToolkitHost,0>) [AssetTypeActions_StaticMesh.cpp:75] UE4Editor-UnrealEd!UAssetEditorSubsystem::OpenEditorForAsset(UObject *,EToolkitMode::Type,TSharedPtr<IToolkitHost,0>,bool) [AssetEditorSubsystem.cpp:363] UE4Editor-UnrealEd!UAssetEditorSubsystem::OpenEditorForAssets_Advanced(TArray<UObject *,TSizedDefaultAllocator<32> > const &,EToolkitMode::Type,TSharedPtr<IToolkitHost,0>) [AssetEditorSubsystem.cpp:437] UE4Editor-UnrealEd!UAssetEditorSubsystem::OpenEditorForAssets(TArray<UObject *,TSizedDefaultAllocator<32> > const &) [AssetEditorSubsystem.cpp:553] UE4Editor-ContentBrowserAssetDataSource!ContentBrowserAssetData::EditOrPreviewAssetFileItems(TArrayView<TSharedRef<FContentBrowserAssetFileItemDataPayload const ,0> const ,int>,bool) [ContentBrowserAssetDataCore.cpp:287] UE4Editor-ContentBrowserAssetDataSource!ContentBrowserAssetData::EditOrPreviewItems(IAssetTools *,UContentBrowserDataSource const *,TArrayView<FContentBrowserItemData const ,int>,bool) [ContentBrowserAssetDataCore.cpp:307] UE4Editor-ContentBrowserAssetDataSource!UContentBrowserAssetDataSource::BulkEditItems(TArrayView<FContentBrowserItemData const ,int>) [ContentBrowserAssetDataSource.cpp:932] UE4Editor-ContentBrowser!SContentBrowser::OnItemsActivated(TArrayView<FContentBrowserItem const ,int>,EAssetTypeActivationMethod::Type) [SContentBrowser.cpp:2238] UE4Editor-ContentBrowser!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,void ,FDefaultDelegateUserPolicy>::Execute(TArrayView<FContentBrowserItem const ,int>,EAssetTypeActivationMethod::Type) [DelegateInstancesImpl.h:290] UE4Editor-ContentBrowser!SAssetView::OnListMouseButtonDoubleClick(TSharedPtr<FAssetViewItem,0>) [SAssetView.cpp:3446] UE4Editor-ContentBrowser!TBaseSPMethodDelegateInstance<0,SAssetView,0,void ,FDefaultDelegateUserPolicy>::ExecuteIfSafe(TSharedPtr<FAssetViewItem,0>) [DelegateInstancesImpl.h:307] UE4Editor-ContentBrowser!TDelegate<void ,FDefaultDelegateUserPolicy>::ExecuteIfBound<void,0>(TSharedPtr<FAssetViewItem,0>) [DelegateSignatureImpl.inl:599] UE4Editor-ContentBrowser!SListView<TSharedPtr<FAssetViewItem,0> >::Private_OnItemDoubleClicked(TSharedPtr<FAssetViewItem,0>) [SListView.h:1074] UE4Editor-ContentBrowser!STableRow<TSharedPtr<FAssetViewItem,0> >::OnMouseButtonDoubleClick(FGeometry const &,FPointerEvent const &) [STableRow.h:458] UE4Editor-Slate!static class FReply FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FPointerEvent,<lambda_2b5148752c2a272000c47b69ff14a42e> >(class FSlateApplication *, class FEventRouter::FBubblePolicy, struct FPointerEvent, const class FSlateApplication::RoutePointerDoubleClickEvent::__l2::<lambda_2b5148752c2a272000c47b69ff14a42e> & const, ESlateDebuggingInputEvent) [SlateApplication.cpp:378] UE4Editor-Slate!FSlateApplication::RoutePointerDoubleClickEvent(FWidgetPath const &,FPointerEvent const &) [SlateApplication.cpp:5281] UE4Editor-Slate!FSlateApplication::ProcessMouseButtonDoubleClickEvent(TSharedPtr<FGenericWindow,0> const &,FPointerEvent const &) [SlateApplication.cpp:5268] UE4Editor-Slate!FSlateApplication::OnMouseDoubleClick(TSharedPtr<FGenericWindow,0> const &,EMouseButtons::Type,FVector2D) [SlateApplication.cpp:5231] UE4Editor-ApplicationCore!FWindowsApplication::ProcessDeferredMessage(FDeferredWindowsMessage const &) [WindowsApplication.cpp:2178] UE4Editor-ApplicationCore!FWindowsApplication::DeferMessage(TSharedPtr<FWindowsWindow,0> &,HWND__ *,unsigned int,unsigned _int64,_int64,int,int,unsigned int) [WindowsApplication.cpp:2638] UE4Editor-ApplicationCore!FWindowsApplication::ProcessMessage(HWND__ *,unsigned int,unsigned _int64,_int64) [WindowsApplication.cpp:1042] UE4Editor-ApplicationCore!FWindowsApplication::AppWndProc(HWND__ *,unsigned int,unsigned _int64,_int64) [WindowsApplication.cpp:874] USER32!7ff892440000 + e858 USER32!7ff892440000 + e4ee InkObj!7ff80c180000 + e7e19 atlthunk!7ff88a090000 + 1028 USER32!7ff892440000 + e858 USER32!7ff892440000 + e299 UE4Editor-ApplicationCore!FWindowsPlatformApplicationMisc::PumpMessages(bool) [WindowsPlatformApplicationMisc.cpp:130] UE4Editor!7ff6d49d0000 + 87e7 UE4Editor!7ff6d49d0000 + 2113c UE4Editor!7ff6d49d0000 + 2121a
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-107204 in the post.