Have a look at [Darktable] Broken 'Pink' highlights and how to fix them - YouTube
You need to spend some effort to correct it.
If you’re using filmicrgb with „max rgb“ you’re reconstruction colors in an area where no valid colors are available.
You might use guided laplacian highlight reconstruction and play around with iterations to mitigate the effect, you can play around with highlight reconstruction in filmic to even mitigate more.
If you need an explanation why all that happens you might spend some time with [EN] Highlights reconstruction : the guided Laplacian - YouTube