Slate disappears from in game screen?

Yes it is member variabled my TestHUD.h looks like this

UCLASS()
class ATestHUD : public AHUD
{
	GENERATED_UCLASS_BODY()

	TSharedPtr<class STestUIWidget > TestUIWidget;

	void BeginPlay();

	void DrawHUD();
	
};

Like I said the knowledge I had of Slates was basically just from the tutorial I followed however I have done more research on them now and well there seems to be a lot more to SWeakWidget than I originally thought.

In terms of just adding the TestUIWidget to the viewport I did try this

GEngine->GameViewport->AddViewportWidgetContent(TestUIWidget.ToSharedRef());

However the result was still the same