Photos App Not Showing Some Photos

I expect this is going to end up costing me a very expensive and ultimately unhelpful call to Apple technical support, but I thought I'd try the community first…

My environment is Apple Photos 8.0 (560.0.110) on a 2019 27-inch iMac running 13.6.6 "Ventura". My Photos library is stored on an external USB SSD formatted as Mac OS Extended (Journaled), with the Ignore ownership on this volume flag set. The problem I'm experiencing also happens under my wife's account on her 2023 Mac Mini (same OS, same version of Photos). We are not using iCloud in any way, not for anything: it is not enabled on our Macs, nor on our iPhones. There have been no changes or updates to either of our Macs at least in the past 12 months. I have already performed a Repair operation on my Photos library. I have surfed the support forums and haven't found anything that seems applicable.

I recently came across a folder of JPG files from Thanksgiving 2023. I opened Apple Photos on my iMac and browsed to the "Thanksgiving 2023" album in order to ensure I had already imported all of them. I noticed a discrepancy of one file (i.e., there were 44 photos in Photos, but 45 JPG files in the folder). After eyeballing, I located the single photo that was in the folder but not in Photos.

In Photos, I went to the File menu, selected Import, and tried to import the missing file. However, a dialog was displayed indicating the photo was already in Photos: the photo was shown in the dialog twice, with the same file name (IMG_2073.JPG) captioning both, and I was prompted whether I still wanted to import the photo! I chose Cancel.

I rechecked the "Thanksgiving 2023" album in Photos and still could not find the photo. I also checked the following locations in Photos:

• • A 2023 smart album that includes all files from 2023
  • The Library of all files
  • The Photos search bar, searching for the file name IMG_2073.JPG
  • The Deleted photos album
  • The Hidden Photo Album (which was empty).

I even went back through the Imports album to 1/24/2023, which was the day when I originally imported the photos. The missing photo doesn't show there, either, as if the photo was never imported! In fact, NOWHERE in Photos is the photo anywhere to be found! Yet, if I attempt to import it, Photos says the photo is already in the library.

To troubleshoot this problem, I opened a Finder window, chose to Show Package Contents on the Photos library file, browsed to the folder named "originals", and then used the finder search bar to search for all files with a creation date of 1/24/2023—the date on which I originally imported all 45 photos. Sure enough, the missing photo is there, shuffled in among the 16 subfolders under "originals", with a mangled file name like all the others. So, the missing photo really is "in" Photos, it just isn't displayed anywhere.

My questions are these:

1. How do I coax Photos to show the missing photo

And much more importantly:

2. How do I go about figuring out what other photos have now "gone missing", in that they are "in" Photos, but aren't being displayed, and get Photos to display them, too?

Please note here that restoring my Photos library from a Time Machine backup isn't an applicable solution in this case. Here's why.

Since there's no way to know what photos are missing, nor when they went missing, there's no way to know what point in time to restore from. Furthermore, the further back in time I have to restore, the more imports I will lose (for example: if I restore from a backup in early September, I will lose all the photos my wife imported from her phone this past weekend.) I can't first export any batches of files I might lose by going to an old restore point, because those batches might contain photos that Photos isn't displaying, and therefore I can't select them for export!

This really is a terrible mess, and completely undermines all of my confidence in Photos as an app.