jbringolf Update - It appears if I delete or add another image, it then sees the new value - does the File Manager cache the IPTC Data?
Files Gallery uses folder cache that refreshes when the folder "modified time" (mtime) changes. In your case, I think your tool is modifying the file without the folder time getting updated, and this means cache may not refresh automatically.
The simple solution is to rename a file in the folder (and rename it back again if necessary), to force the folder cache to refresh. Optionally, you could do touch path/to/folder
in command line to update the "modified time".