I'm using Photo Mechanic Version 6.0, build 5404 (e13fb4f), on macOS 10.15.6
For photos that have overexposed regions, PM renders them in black instead of white. As far as I can tell, this is a PM issue - both system preview and Lightroom handle the image just fine. Screenshots attached. (11.28.58: As rendered by PM. 11.29.19: As rendered by system preview. IMG_2304.JPG: Original image, in case there's any additional metadata that's helpful for your debuggin)
I *suspect* it's color correction, though turning it off in preferences doesn't fix the problem.