If an actor contains a custom SceneComponent that creates another component that is tagged with Transient and DuplicateTransient, deleting/un-deleting/deleting the actor again will cause the editor to crash.
This also causes the project to reach 95% when loading and then produce the same callstack.
Workaround:
Crash only seems to occur if the component that is declared in the custom scene component is marked as Transient and DuplicateTransient in its UPROPERTY macro.
UPROPERTY(Transient, DuplicateTransient) UStaticMeshComponent* MeshComponent;
TheMeshComponent = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("TheMeshComponent"));
Result:
Editor crashes when trying to delete the actor again.
MachineId:9FA88CA44B7C623122B0039D6C8BA1B0 EpicAccountId:c807849e05a0413d99e379f2802cae9c Unknown exception - code 00000001 (first/second chance not available) "Assertion failed: ChildCount > AttachChildren.Num() [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.10\Engine\Source\Runtime\Engine\Private\Components\SceneComponent.cpp] [Line: 680] Att UE4Editor_Core!FDebug::AssertFailed() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\core\private\misc\outputdevice.cpp:374] UE4Editor_Engine!USceneComponent::OnComponentDestroyed() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\components\scenecomponent.cpp:680] UE4Editor_Engine!UActorComponent::DestroyComponent() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\components\actorcomponent.cpp:946] UE4Editor_Engine!AActor::DestroyConstructedComponents() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\actorconstruction.cpp:163] UE4Editor_Engine!AActor::RerunConstructionScripts() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\actorconstruction.cpp:354] UE4Editor_Engine!ULevel::IncrementalUpdateComponents() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\level.cpp:783] UE4Editor_Engine!UWorld::UpdateWorldComponents() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\engine\private\world.cpp:1321] UE4Editor_UnrealEd!UEditorEngine::Map_Load() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\editorserver.cpp:2479] UE4Editor_UnrealEd!UEditorEngine::HandleMapCommand() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\editorserver.cpp:5897] UE4Editor_UnrealEd!UEditorEngine::Exec() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\editorserver.cpp:5391] UE4Editor_UnrealEd!UUnrealEdEngine::Exec() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\unrealedsrv.cpp:743] UE4Editor_UnrealEd!FEditorFileUtils::LoadMap() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\filehelpers.cpp:2014] UE4Editor_UnrealEd!FEditorFileUtils::LoadDefaultMapAtStartup() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\filehelpers.cpp:3215] UE4Editor_UnrealEd!FUnrealEdMisc::OnInit() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\unrealedmisc.cpp:299] UE4Editor_UnrealEd!EditorInit() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\editor\unrealed\private\unrealed.cpp:86] UE4Editor!GuardedMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\launch\private\launch.cpp:133] UE4Editor!GuardedMainWrapper() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\launch\private\windows\launchwindows.cpp:126] UE4Editor!WinMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.10\engine\source\runtime\launch\private\windows\launchwindows.cpp:200] UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264] kernel32 ntdll
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-25780 in the post.