Bug - Hiss Reduction > Capture Noise Floor

With all due respect, this^ is just not true. If you make a noise selection with the left channel selected, then yes, you will see nothing. But if you now select the right channel, you'll see the noise profile you just created, even though you thought it was from the left. And if you apply it, you'll see it applied to both channels. What's actually 'wrong' is that there's a channel selection at all - it really doesn't need to be there.

What is happening is just the same as happens with process NR. A single FFT profile is created and applied to both channels. If you had a separate one for each channel, whenever there was a difference between one channel and the other there would be a shift in the stereo noise floor, which you wouldn't want. That is why there are only single Noise Floor and  Reduce by sliders, and no splitting.

Yes I agree that the screen layout is, to say the least, a bit confusing. But it is working correctly.

It works fine here - latest build on W10. I have no idea of the situation as far as Macs are concerned. By design it only appears to capture noise from the left or right, but careful observation of the results shows that the effect is applied to both channels. Almost invariably you have to edit the noise floor control until the hiss goes away - this is with a check in the Output Hiss Only box. If you don't do this correctly then it won't work.