@Tom I am a Windows user and there are differences between DxPL on the Mac and on Windows but I believe that on both systems the presence or absence of a directory, as far as DxPL is concerned; is based not on the drive name, e.g. D:\ etc, but on the drive identifier.
This is shown as the UniqueId in the following snapshot of the ‘Folders’ structure (there are structure name and field name differences between Mac and Windows but they are fairly similar in structure)
It is that field that DxPL uses to locate (or not) any existing entries in the database, if there is no match then DxPL will add that folder to ‘Folders’ and start discovering the images as if it has never seen them before.
If all your old files now reside on a drive with a different identifier than when you first discovered them in DxPL, then those old discoveries will remain in the database and DxPL will discover them “afresh” when you look at the folders on the new drive and create new entries!
My guess is that the images that you can see “correctly” are the new images and the old images are showing as Black with a question mark, not the other way around!
So a little test with 3 directories named Ben, Bill and Little Weed (look up “The FlowerPot Men” fir information on this “ancient” children’s TV program!
Each has the same 4 images and are assigned keywords relating to their location (“Ben”, “Bill” and “Little Weed”). Each group of four are also assigned to a Project, named, you guessed it already.
So we have
While PL8 is occupied with another directory two images were deleted from Ben, 2 from Bill and all from Little Weed using file manager but the search function is based on the state of the database and searches immediately yield the following
Following the Projects links yield this
and the re-discovery and searches yield this
I have recreated the symptoms of the problem not the exact cause but on Windows and Mac the ‘Projects’ will be useless because the pointers are to database entries that no longer have “real” entries available and the same thing happens with searches because they discover the new entries but also the old ones!
PS:- I might be wrong because your “missing” is black with a question mark and mine also have an exclamation mark and the symbol to identify that the camera/lens combination is unknown!?