Problem with noisy shadows in alpha channel - ShadowCatcher

Hi, I have a problem with noise in alpha channel.
I am using shadowcatcher (set to cmopisiting), to get shadows without background.
When the render is done and I am saving it to .png- all is denoised fine but the shadows are not.
In Beauty channel all looks great.
Is there a way to denoise alpha channel?

Cinema R19 Studio, Corona 6.

Hi
I have the same issue, have you found a solution ?
thank you kindly