Upgraded from LR5 to Classic - issues

Hi

I've just upgraded to LR Classic - following the prompts that appeared to update the catalogue. Now, every image not on the local harddrive shows as blank in Library - there is no ? indicated nor option to locate the image. The 'Show In Finder' works as it should, and shows the image in the folder. I've attached a screenshot of how it looks. At present I can't view, edit or export the images.

Any help much appreciated, thanks

Mark