Duplicated files when importing

I have a folder which I’m trying to import (Add), but although it has the right number of files it’s duplicating some and not adding others.

I have removed the folder and tried again once as the same folder and a second time after copying the folder to a different location and with a new name and the result is the same each time.

The files are jpeg converted from RAW in Canon DPP software which I always do and have added 4 other folders without any problem.