It's known that dual_iso dng files cause artifacts when converted to lossy dng in the regions of deep shadows that have been interpolated as half the the scanlines were clipped in the original raw file.
Apart from just being a "missing dng feature" in comparison to vanilla raw files, this problem has become more severe in recent Adobe apps since it's the base for the offline "smart preview" files. The free dng converter can be used to convert dng to lossy w/o Photoshop or Lightroom, it's basically 8bit jpeg-derived compression with the added benefit of keeping lossless wb adjustment.
I hope there's a way to do a minor cr2hdr adjustment to circumvent this problem. Alas, as Adobe's compression algorithm is closed source it might be tricky to identify the exact cause of the problem, but imho it's well worth a try. The dng converter seems to erroneously identify and compress these specific regions, maybe adding some noise or similar could be added to prevent this from happening?