This sounds like one of the many import bugs in the latest LR CC. I recommend you revert to 2015.1.1 (instructions here: http://www.lightroomqueen.com/how-do-i-roll-back-to-lightroom-2015-1-1-or-lightroom-6-1-1/ ) and check if this is still a problem.
if you don't want to revert right away you can also try to turn off the "show add photos screen" in preferences-> general. This circumvents a few of the bugs Like this. However, Adobe is bringing back the old import screen soon, so maybe not so necessary to get used to the new screen.
Thanks for your answer.
I followed the instructions although with one error ( I also installed the first patch on the list).
I am now at the 2015.1.1 version, but this has not solved the problem. I also now have another problem in that the histogram in the Library mode is no longer displaying which leaves me puzzled.
As I run Windows 10 and that seems to update automatically, I am now wondering if something in W10 is stopping LR from seeing newly copied files in the library.
Any further suggestions on where to look will be gratefully accepted.
I did try initially to disable the show add photos screen without any improvement.
Do you have a filter enabled in the grid view by any chance?
Thanks for your reply.
I eventually managed to locate the problem, which seems to have been due to LR having difficulty locating files correctly on my NAS. I eventually changed LR to point to my NAS photos folder using it as a mapped drive. Originally it was using the path. Probably my error in setting it up.
Certainly though whatever, going back to the 2015.1.1 version does also make life easier. The only question will remain as to how we will know if and when Adobe gets around to fixing the problem with the latest LR version?