This problem often arises in Universal Windows Platform (UWP) development when trying to use a CompositionEffectBrush directly as the fill for a CompositionSpriteShape.

To achieve an irregular-shaped blur:

• CompositionSpriteShape can only be filled with a CompositionColorBrush or a CompositionSurfaceBrush (e.g., loaded from a file or created via CompositionDrawingSurface). It cannot directly use a CompositionEffectBrush.

• You must bind the shape to a CompositionContainerShape that is parented by a CompositionVisual (like a SpriteVisual Bazoocam).

• Apply the CompositionEffectBrush to the SpriteVisual.Brush property instead.

• Use the CompositionSpriteShape (with an opaque fill like a CompositionColorBrush ) as the mask by applying the CompositionContainerShape to the SpriteVisual.Clip property or, more robustly, by using a CompositionGeometricClip.