Today’s Question: There is another possibility here [with respect to Monday’s question about not being able to move a file into a folder because Lightroom Classic thinks the image is a duplicate when it isn’t]. A file may have been removed from Lightroom Classic but not deleted from the hard drive. As a result, the photo is still in the folder but not visible through the Lightroom Classic interface.
Tim’s Quick Answer: Yes, indeed, if photos had been removed from the Lightroom Classic catalog but not deleted from the hard drive, it could create a situation where you can’t move a photo into a folder, even though in Lightroom Classic it doesn’t appear there is a conflict.
More Detail: When you remove a photo from your Lightroom Classic catalog, you have the option to only remove the photo from the catalog, or to both remove the photo from the catalog and delete the source image from your hard drive.
If you only remove the photo without deleting it (which is the default option), the file will remain in the folder even though you can’t see the image in Lightroom Classic. This would prevent you from moving a photo with the same filename into that folder, even though in Lightroom Classic there doesn’t appear to be a conflict.
In this case, you would probably want to delete the photo that had previously been removed from your Lightroom Classic catalog from your hard drive. You could also rename the photo to remove the conflict, or even add the removed photo back to your Lightroom Classic catalog by right-clicking on the folder in question and choosing the option to synchronize the folder.
While I wish I hadn’t overlooked this issue in my original answer, I’m grateful to my readers (thanks Bob!) who let me know when I missed a detail.