For some strange reason DxO PhotoLab 5.1.1 seems to fail to read the list of files in a folder in the PhotoLibrary. Restarting does not seem to help either - very strange.
I found if I close PL5 and then rename the folder and open PL5 again it will the read all the files correctly and list then in the photoLibrary
The latest version for Mac is v5.1.1.
…/100MSDCF is a folder on the SD card of a Sony camera ?
Are you reading your files from the SD card ? or on your camera via USB ?
How are you creating the folder to receive the files?
What camera?
Are you reading from the camera via a USB cable or from the memory card in an adapter?
Did you know macOS has a little app called Image Transfer that you can use to transfer files directly from the camera, via a USB cable, to the folder of your choice?
The same way I have always copied them, via USB cable direct from the camera and drag and drop the folder to the laptop SSD. Never had this problem prior to v5.x so I think it is PL5 that does not refresh the folder contents after reading the folder the first time.