hello,
last Thursday I have updated to macOS Catalina (10.15.1) and Photo Mechanic Version 6.0, build 3889 (6e9c549) has quite some problems with "Capture Time" sorting of the photos in the contact sheet - had the problem after opening folder with newly exported photos as well as with a folder which was already opened, with some photos in it and then some more photos were exported into this folder - sometimes it helps just to click on the "Capture Time" drop down "button", but sometimes it doesn't help, on some occasions it would even shuffle the sort order a little bit when going through the photos ...