Unfortunately, I cannot upload any of the images on which I actually ran into the problem. Legal reasons.
But I don't think it has anything to do with the content of the photo.
Looking back at the very first photoshoot affected, it was the fourth picture taken and the first picture that I tried to scale which caused the problem.
I exported six different crops from the photo of various portions of the image and at various resolutions. Then I ran into the bug with that image and it has been present ever since.
Today, after my computer has been restarted, the bug isn't showing up when just looking at images and pretending to crop them without actually doing it.
I'm relying on your expertise to figure this one out, because it's not reproducible except in real life.
Most likely if you duplicate the image I attached and make 10-20 copies of it, and start going through them like you were really doing work, cropping in every possible combination of coverage of the image, and every possible combination of everything else, you would run into the issue right away.
I'm using the latest version of Mojave, with the latest version of the iMac, 64 GB of RAM and the best graphics card. So it shouldn't be an issue of computing resources available.