Lightroom to import thousands again. Don't Import Suspected Duplicates checked.

[CMAmuseumbrich4d]

What would cause my catalog want to import thousands of photos that have already been imported? I have checked "Don't Import Suspected Duplicates". On a recent import of a new folder, it imported those images but it moved the folder to the top of the folder structure. This folder should be three folders deep where it is located on the harddrive.
I have over 139000 images imported and this is the first probably I have run into. My catalog was updated in early December to be compatible with Lightroom Classic 9.0 and it has worked fine for the past month and a half. I did a test on only one folder of images that it wanted to import as duplicates and out of the 130 images in the folder it said 13 were never imported and I verified that they previously had. They are not corrupt, too.
I did update to Lightroom Classic 9.1 today to see if that corrected the issue but it has not.
Thank You,
Lightroom Classic 9.1
macOS High Sierra 10.13.6
MacPro (Mid 2012)
96GB Ram

[rdonson]

Silly question.  Are the file names the same?

[CMAmuseumbrich4d]

Names are exactly the same. And when you do a reveal in finder for the correct location and the odd location they refer to the same single file of that name.

[FabienP]

AFAIK Lightroom does not rely on filenames to detect potential duplicates. Files are hashed and any matching file signature will be declared as duplicate. This is the reason why the import takes such a long time to find matches: all files on the source / import card need to be read and hashed to find duplicates.

One use case where files would not match is if you are transforming RAW files into DNG files, which then get changed after the import (new metadata added to the DNG files). This assumes that the whole file is hashed and not just the image part, I don't know if this is the way Lr works.

I would try to manually produce hashes of file pairs to assess if the files are really identical. Any programme producing md5, sha1 or sha256 hashes could be used for that purpose. That would at least rule this potential issue out.

Cheers,

Fabien