Using flipbook material with Slate Brush for loading screen

I want to replace a sequence of texture images used in a Slate Widget for an animated loading screen image by a UI Material using a flipbook texture. I am using the MoviePlayer API for the Loading Screen to make this async.

The Material looks as follows and works perfectly in UMG:

The Slate Brush is defined as follows

struct HENRYLOADINGSCREEN_API FFlipBookBrush : public FSlateBrush, public FGCObject
{
	FFlipBookBrush(const FName InMaterialName, const FVector2D& InImageSize)
		: FSlateBrush(ESlateBrushDrawType::Image, InMaterialName, FMargin(0), ESlateBrushTileType::NoTile, ESlateBrushImageType::FullColor, InImageSize, FLinearColor(1, 1, 1, 1))
	{
		SetResourceObject(LoadObject<UObject>(NULL, *InMaterialName.ToString()));
	}

	virtual void AddReferencedObjects(FReferenceCollector& Collector)
	{
		if (UObject* CachedResourceObject = GetResourceObject())
		{
			Collector.AddReferencedObject(CachedResourceObject);
		}
	}
};

And the SImage using the material is created as follows (still hardcoded name for testing)

FlipBookBrush = MakeShareable(new FFlipBookBrush(FName(/Game/Henry/UI/Flipbook-material/M_ChickenFlipbook.M_ChickenFlipbook), FVector2D(96, 96)));
FlipBookMat = SNew(SImage).Image(FlipBookBrush.Get());

When I add this to the Widget, it does not work as expected. It does not matter whether I derive the brush from FSlateBrush or from FSlateMaterialBrush. In both cases:

  • For a loading screen loaded at game load time (module load), nothing is rendered at all.
  • For an In Game loading screen at level change only one of the images (not the first one) is shown frozen and no animation happens at all.

I almost get the impression, that using Flipbook materials with Time node is not a supported thing for Slate Widgets running on a separate thread with MoviePlayer, and that I must keep going on with a series of Texture Images updated using OnPaint() override.

Is my assumption correct or am I still missing something here?

Is there really no one who ever tried to use a Flipbook material with Slate to create a brush. I revisited this again, but still found no solution.
The Docs for Blueprint node MakeBrushfromMaterial say

Creates a Slate Brush from a Material. Materials don’t have an implicit size, so providing a widget and height is required to hint slate with how large the image wants to be by default.

Means, that it should be supported. And it looks like this is only for passing in the size - in my case, this is ok, because that ‘frozen’ image I see is in correct size.