CUDA + Fast Box Blur + Curves – Alpha Channel Bug

Issue – bear with me, it's complicated to describe:

The computation result of layers that have a Fast Box Blur, and subsequent masked Curves effect applied, is offset by an unknown amount that is relative to the mask's top edge – see screenshots. This issue only occurs when Mercury GPU acceleration (CUDA) is enabled.

While narrowing down the issue, AE started throwing the "GPU Effects Error" erratically. Sometimes after duplicating a composition, and other times right upon loading the project.

Steps to reproduce:

1. apply a Fast Box Blur effect to a layer
2. add a Curves effect
3. trace an additive mask, that spans from the centre of the object down to the bottom of the composition, and spans across the entire width of the composition
4.  switch the curves effect channel to Alpha, trace an S-Curve
5. set the mask as compositing mask for the Curve effect

AE Version: 23.4.0 (Build 53)

Platform: Windows 11 Pro (Build 22621.1702)

NVIDIA Studio Driver: 531.61 & 535.98

Expected Result – with GPU acceleration enabled: the desired result can be achieved when using a Levels effect, instead of a Curves effect; Or using a Gaussian Blur effect, instead of the Fast Box Blur effect. The attached project contains two compositions with the desired result.