This is a somewhat common crash coming out of the 4.17 release.
User Descriptions
Source Context
4579 for (int32 i = 0; i < Linker->ExportMap.Num(); i++) 4580 { 4581 FObjectExport& Export = Linker->ExportMap[i]; 4582 if (Export.Object) 4583 { 4584 // Set class index. 4585 // If this is *exactly* a UClass, store null instead; for anything else, including UClass-derived classes, map it 4586 UClass* ObjClass = Export.Object->GetClass(); 4587 if (ObjClass != UClass::StaticClass()) 4588 { 4589 Export.ClassIndex = Linker->MapObject(ObjClass); 4590 check(!Export.ClassIndex.IsNull()); 4591 } 4592 ***** else 4593 { 4594 Export.ClassIndex = FPackageIndex(); 4595 } 4596 4597 if (IsEventDrivenLoaderEnabledInCookedBuilds() && TargetPlatform) 4598 { 4599 UObject* Archetype = Export.Object->GetArchetype(); 4600 check(Archetype); 4601 check(Archetype->IsA(Export.Object->HasAnyFlags(RF_ClassDefaultObject) ? ObjClass->GetSuperClass() : ObjClass)); 4602 Export.TemplateIndex = Linker->MapObject(Archetype); 4603 UE_CLOG(Export.TemplateIndex.IsNull(), LogSavePackage, Fatal, TEXT("%s was an archetype of %s but returned a null index mapping the object."), *Archetype->GetFullName(), *Export.Object->GetFullName()); 4604 check(!Export.TemplateIndex.IsNull()); 4605 }
repro steps currently unknown
Assertion failed: !Export.ClassIndex.IsNull() [File:D:\Build\++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\SavePackage.cpp] [Line: 4591] UE4Editor_CoreUObject!UPackage::Save() [savepackage.cpp:4593] UE4Editor_UnrealEd!UEditorEngine::Save() [editorengine.cpp:4210] UE4Editor_UnrealEd!UCookOnTheFlyServer::SaveCookedPackage() [cookontheflyserver.cpp:3238] UE4Editor_UnrealEd!UCookOnTheFlyServer::SaveCookedPackages() [cookontheflyserver.cpp:2324] UE4Editor_UnrealEd!UCookOnTheFlyServer::TickCookOnTheSide() [cookontheflyserver.cpp:1786] UE4Editor_UnrealEd!UCookOnTheFlyServer::Tick() [cookontheflyserver.cpp:879] UE4Editor_UnrealEd!FTickableEditorObject::TickObjects() [tickableeditorobject.h:21] UE4Editor_UnrealEd!UEditorEngine::Tick() [editorengine.cpp:1424] UE4Editor_UnrealEd!UUnrealEdEngine::Tick() [unrealedengine.cpp:402] UE4Editor!FEngineLoop::Tick() [launchengineloop.cpp:3215] UE4Editor!GuardedMain() [launch.cpp:166] UE4Editor!GuardedMainWrapper() [launchwindows.cpp:134] UE4Editor!WinMain() [launchwindows.cpp:210] UE4Editor!__scrt_common_main_seh() [exe_common.inl:253] kernel32!BaseThreadInitThunk() ntdll!RtlUserThreadStart()
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-50093 in the post.