When using the denoiser render element on scenes with transparent alpha, it used to be that you would get an RGB with alpha shadow, not denoised.
Then the same RGB with alpha shadow, denoised and labelled EffectsResult. This was great because we could blend the two versions in post, since the denoiser on the shadow is sometimes too much and it wrecks the alpha edge causing all sorts of jagged edges and halos.
However, now the denoiser is applied to the alpha shadow on both the RGB and the EffectsResult render elements. This is such a pain because the shadow especially matte shadows, after all these years still render like crap and very, very noisy. Even with noise threshold at 0.005, even 0.002 .
Since the denoiser causes havoc with the alpha mask causing jagged edges and halos. So we end up rendering the image twice, one with denoiser and one without, so that we get both passes. We can then blur the shadow in post to get rid of the noise and maintain a nice alpha edge.
Not sure why it changed, so now denoiser is applied to alpha shadow regardless. But its frustrating.
We render on the Chaos Cloud, therefore we cannot use tricks like individually increasing the subdivs multiplier on the mate shadow ground plane. This setting seems to be ignored. So we are stuck with very noisy shadows and have to find work arounds all the time.