Parent class of my widget blueprint class which has native c++ parent class, is set to none

Based on the contents below, I created a blueprint class and am working on moving it to c++ class.

C++ class’s logic is same with blutprint class.

I design widget blueprint class and reparent to c++ class.

here is c++ code

CompassBar.h

#pragma once

#include “CoreMinimal.h”
#include “Blueprint/UserWidget.h”
#include “CompassBar.generated.h”

class UMaterialInstanceDynamic;

UCLASS()
class STRUGGLELIFE_API UCompassBar : public UUserWidget
{
GENERATED_BODY()

protected:
virtual void NativeConstruct() override;

virtual void NativeTick(const FGeometry& MyGeometry, float InDeltaTime) override;

UPROPERTY()
UMaterialInstanceDynamic* CompassMaterial;

};

CompassBar.cpp

#include “CompassBar.h”
#include “Components/Image.h”
#include “Kismet/GameplayStatics.h”

void UCompassBar::NativeConstruct()
{
Super::NativeConstruct();

UImage* CompassBar = Cast<UImage>(GetWidgetFromName("DSN_CompassBar"));

if(CompassBar)
{
	CompassMaterial = CompassBar->GetDynamicMaterial();
}

}

void UCompassBar::NativeTick(const FGeometry& MyGeometry, float InDeltaTime)
{
Super::NativeTick(MyGeometry, InDeltaTime);

APlayerController* PlayerController = UGameplayStatics::GetPlayerController(GetWorld(), 0);

const FRotator ControllerRotation = PlayerController->GetControlRotation();
	
const float CompassRatio = ControllerRotation.Yaw / 360.f;

CompassMaterial->SetScalarParameterValue("YawRatio", CompassRatio);

}

It works, but if i reopen editor widget blueprint class’s parent is set to none

I don’t know why, and would you please give me some advice?