So, this happened to me again, and in the same circumstances. I added some face annotations to an image while in the viewer, and when I closed the viewer, and IMatch shut down with no error messages. This time I did have the log in debug mode.
Nothing to see in the log file.
IMatch was updating collections when the log file stopped. No errors. No warnings.
Did IMatch not create a DUMP file? See The Debug Dump File (https://www.photools.com/help/imatch/#im_dumpfile.htm)
No, there was no dump file.
Hm...
No errors. No warnings (except some from ExifTool about invalid date and time in some of your files, but that's not uncommon).
IMatch closes without warning. Neither Windows nor IMatch reports an error (message box)?
No idea, sorry.
Okay. If I come up with any more clues, I'll post again.