This is the top of the call stack when the exception is thrown:
> UE4Editor-Engine.dll!UParticleSystemComponent::DeactivateSystem() Line 5842 C++
UE4Editor-ace-6854.dll!AacePawn::AacePawn() Line 77 C++
UE4Editor-CoreUObject.dll!StaticConstructObject_Internal(UClass * InClass, UObject * InOuter, FName InName, EObjectFlags InFlags, EInternalObjectFlags InternalSetFlags, UObject * InTemplate, bool bCopyTransientsFromClassDefaults, FObjectInstancingGraph * InInstanceGraph, bool bAssumeTemplateIsArchetype) Line 3156 C++
UE4Editor-CoreUObject.dll!FDuplicateDataWriter::GetDuplicatedObject(UObject * Object, bool bCreateIfMissing) Line 138 C++
UE4Editor-CoreUObject.dll!FDuplicateDataWriter::operator<<(UObject * & Object) Line 65 C++
[Inline Frame] UE4Editor-Engine.dll!operator<<(FArchive &) Line 92 C++
UE4Editor-Engine.dll!operator<<(FArchive & Ar, TArray<AActor *,FDefaultAllocator> & A) Line 1109 C++
UE4Editor-Engine.dll!ULevel::Serialize(FArchive & Ar) Line 316 C++
UE4Editor-CoreUObject.dll!StaticDuplicateObjectEx(FObjectDuplicationParameters & Parameters) Line 2094 C++
UE4Editor-CoreUObject.dll!StaticDuplicateObject(const UObject * SourceObject, UObject * DestOuter, const FName DestName, EObjectFlags FlagMask, UClass * DestClass, EDuplicateMode::Type DuplicateMode, EInternalObjectFlags InternalFlagsMask) Line 2000 C++
UE4Editor-UnrealEd.dll!UEditorEngine::CreatePIEWorldByDuplication(FWorldContext & WorldContext, UWorld * InWorld, FString & PlayWorldMapName) Line 3656 C++
UE4Editor-Engine.dll!UGameInstance::InitializeForPlayInEditor(int PIEInstanceIndex, const FGameInstancePIEParameters & Params) Line 245 C++
It seems there is a problem with getting the world pointer in DeactivateSystem().