Dwright, I have just experimented by having Affinity bring in the same photo directly from the disk original and it worked without the blown highlights appearing as black. Before I was using ON1 Browse to open the image in AP. I don't know what the difference is, but the problem appears to be on the ON1 side! Thanks for standing by to help! I'll do more experimenting to see if I can narrow it down before contacting ON1.
When I bring a .dng file into AP it immediately displays the blown highlights in black. I cannot seem to get rid of these black marks in the highlight areas and they carry over when the .dng is developed and saved. I have my develop persona set for "take no action" for tone curve and exposure bias, but it doesn't seem to correct the problem when these settings are changed.