Import copies files but doesn't add to library - Windows

I've used Lightroom for years with exactly the same setup. Just recently I have experienced problems with importing. I always import from the SD card to Lightroom using the Copy option. This puts the files in the right folder and the Previous Import count goes up, and the view in Lightroom populates with the images. Now, the copy process will copy the files to the correct folder, but the Previous Import count remains at 0 and the view is empty. If I then use the Add option I can add them from their new location, but it's frustrating to have to do that. 

Has anyone else experienced the same thing? Any ideas how to resolve it? I've gone through the usual obvious things, such as unticking the "Don't import suspected duplicates" box. It's clearly thinking that it's importing, but failing to update the catalog database. TIA