FSlateDrawElement::MakeBox does not render UMaterialInstanceDynamic

Development Rendering
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1

I’m trying to render a dynamic material instance in a Slate Widget and nothing is displayed.

I have a widget derived from SImage

class KSGM_API SKBatteryWidget : public SImage
{
public:
	SLATE_BEGIN_ARGS(SKBatteryWidget)
		: _HUD(nullptr)
		, _BatteryBrush(nullptr)
		, _FillMatInst(nullptr)
		, _Level(1.0f)
		, _MaxLevel(1.0f)
	{}

		/** @brief The HUD used to create the dynamic material instance. */
		SLATE_ARGUMENT(AKPlayerHUD*, HUD)
		/** @brief The battery brush. */
		SLATE_ATTRIBUTE(const FSlateBrush*, BatteryBrush)
		/** @brief The fill material instance. */
		SLATE_ARGUMENT(UMaterialInstance*, FillMatInst)

In the constructor, I create the dynamic material instance using the HUD pointer.

void SKBatteryWidget::Construct(const FArguments& InArgs)
{
	// Create the dynamic material instance
	if (InArgs._HUD != nullptr && InArgs._FillMatInst != nullptr)
		FillMatInstDyn = UMaterialInstanceDynamic::Create(InArgs._FillMatInst, InArgs._HUD);

	Level = InArgs._Level;
	MaxLevel = InArgs._MaxLevel;

	LevelParamName = InArgs._LevelParamName;
	MaxLevelParamName = InArgs._MaxLevelParamName;

	SImage::Construct(SImage::FArguments()
					  .Image(InArgs._BatteryBrush)
					  );

}

In the Tick function, I calculate the ratio and set the parameter to the dynamic material instance.

void SKBatteryWidget::Tick(const FGeometry& AllottedGeometry, const double InCurrentTime, const float InDeltaTime)
{
	SLeafWidget::Tick(AllottedGeometry, InCurrentTime, InDeltaTime);

	CachedGeometry = AllottedGeometry;
	// Calculate the ratio
	float v = Level.Get();
	float m = MaxLevel.Get();
	Ratio = v / m;

	if (FillMatInstDyn)
	{
		FillMatInstDyn->SetScalarParameterValue(LevelParamName, v);
		FillMatInstDyn->SetScalarParameterValue(MaxLevelParamName, m);
	}
}

In the OnPaint call-back, the brush of the battery is well displayed, but the dynamic material instance not.

int32 SKBatteryWidget::OnPaint(const FPaintArgs& Args, const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 LayerId, const FWidgetStyle& InWidgetStyle, bool bParentEnabled) const
{
	LayerId = SImage::OnPaint(Args, AllottedGeometry, MyClippingRect, OutDrawElements, LayerId, InWidgetStyle, bParentEnabled);

	// Draw inside the battery based on the ratio
	FSlateBrush FillBrush;
	FillBrush.SetResourceObject(FillMatInstDyn);
	FillBrush.DrawAs = ESlateBrushDrawType::Image;
	// Calculate the rect we have to fill
	FSlateRect rect = MyClippingRect;
	float height = rect.GetSize().Y;
	rect.Top = rect.Bottom - (Ratio * height);

	LayerId++;

	FSlateDrawElement::MakeBox(
		OutDrawElements,
		LayerId,
		AllottedGeometry.ToPaintGeometry(),
		&FillBrush,
		rect,
		ESlateDrawEffect::None,
		FillBrush.GetTint(InWidgetStyle) * InWidgetStyle.GetColorAndOpacityTint()
		);

	return LayerId;
}

Do I’m missing something or there is a bug rendering dynamic material instance in Slate Widget ?

Txs for your help,
D.