I suppose your struct locates in a UCLASS() as member variable.
Without any initialization it works for me:
USTRUCT(BlueprintType)
struct FMyStruct
{
GENERATED_BODY()
UPROPERTY(BlueprintReadWrite, EditAnywhere)
FTransform Bar;
};
UCLASS()
class CONTENTEXAMPLESCPP_API AMyActor : public AActor
{
GENERATED_BODY()
UPROPERTY(EditAnywhere)
FMyStruct Foo;
public:
AMyActor();
protected:
virtual void BeginPlay() override;
public:
virtual void Tick(float DeltaTime) override;
};