First of all, thanks so much for all the suggestions!
Jack, I have now tried most of what you have suggested, except one, which is how do I check the red channel in Capture One? I have to admit I don't know where or how to do that in the program.
On checking all the other things, and changing them to the various options suggested, the result is pretty much the same. However, I am glad you agree that something is wrong, as it definitely is. I did send an email to Phase One about it, but so far only a confirmation that they received it.
I also contacted my local dealer, and he suspects that because I am using a very recent 12 core Mac, that there is likely a bug that hasn't been addressed yet. A few months ago, prior to the latest upgrade in Capture One, there were a lot of issues.
How can I edit the camera profile? I think that might be a solution.
Regards,
Geoff