I Removed files from Lightroom CC Classic but was unable to re-import them
I recently had trouble with my Import Destination settings and ended up with about seventy files in three folders somewhat jumbled. I think I have now resolved that problem, but on the night I decided that the simplest way for me to restore order would be to Remove the files in question from Lightroom (mostly unprocessed), together with their date folders, use Windows File Explorer to tidy up the files on disc and then reimport the lot.
Files and folders vanished from the Folders panel. I did my bit with File Explorer but when I came to import them all the the thumbnails were greyed out and I was unable to Add them to the catalogue even after unchecking the "no duplicates" box. I presume they were still in the catalogue in some sense. I couldn't find a way to proceed and eventually I turned the machine off for an hour. When I came back I did some general housekeeping, ran AVG Tune Up ditching everything I dared and tried again, this time succeeding at the first attempt.
The problem I'm left with it not understanding why I was originally unable to reimport the files. I've done this sort of thing in the past without difficulties - what might have happened this time? Is there a way to guard against any repetition?