I read that GUI is unsupported. I downloaded it [again] and got it working.
Does GUI display all the tags? I can't find "ExitPupilPosition" or "FocusDistance"...
I don't know the GUI well, but I thought it showed all tags that exifTool itself can show. Are these tags present when you run exiftool on the command line? If not then the GUI won't show them either.