Chroma smooth works without dual iso but i guess it isn't meant to be applied after dual iso post process. because same thing happens with other crop modes.
Focus pixel removal on dual iso should be done
before it is processed. To get a better understanding why read the
Dealing with Focus Pixels in raw video topic.
Start from this post and read the following several replies.
Focus pixel removal is basically chroma smoothing applied to specific areas instead overall. For example, let's zero in on a focus pixel and the pixels immediately adjacent to that focus pixel.
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0 | 0 | 0Averaging in the color of the surrounding pixels will hide that focus pixel. However, focus pixels are often in diagonal pairs which means that averaging in the diagonally adjacent pixels won't work.
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X | 0 | 0With dual iso every pair of rows is a different iso. Why not every row? Because of the Bayer pattern of raw video.
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X | 0 | 0So what happens if your subject happens to have a high contrast vertical line in it that is right next to that focus pixel in the middle of this illustration?
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X | 0 | 1Here is an example of what happens if you average the adjacent pixels on dual iso:

As you can see, dealing with focus pixels with dual iso is challenging.