Problem with Save a copy of files locally setting - not working

I'm having a problem with saving a copy of files locally.  It seemed to be working.  However, I replaced the drive I save to and am trying to copy all my files again.

Lightroom seems to only make a copy when I modify the image e.g. change the exposure under Edit / Light.  Changing metadata, such as the Caption, doesn't trigger the copy.

Any thoughts?

Thanks,

David