Hi all!
Note that when you change anything in LightMix, the VFB automatically switches over to the LightMix view and not the Beauty pass view (you can switch back at any time using the dropdown list). Also, be sure to enable denoising for each LightSelect element, you have to do that for each one individually, then the LightMix view (and individual LightSelect passes) will be denoised.
Also note this applies to 1.5 in 3ds Max - Corona for C4D current daily doesn't have denoising for the LightSelect elements.