I am using the latest version of LR (which is fully updated on a CC subscription) on a 2013 iMac.
When I try to synchronise any of my folders the pop-up dialogue box indicates all the images in the folder require import, and also that the same number of images are missing from the catalog. I discovered this when trying to sync a folder in which a new file had been added from outside of LR and I wanted to bring into my catalog. I always manage my images from within LR and I have not renamed, moved or otherwise altered any images in my catalog outside of LR.
None of the images in LR are flagged as missing, and all are correctly found if I right click and select "Show in finder" or "Show in folder".
Obviously I don't want to reimport the images and remove the supposedly missing photos to complete the synchronisation as I will loose my edits and virtual copies. I did however try this on a folder containing only a small number of images which were not important. This resulted in the folder being moved to the top of the folder listing above the parent folder! LR will not let me move these pictures back into the original parent folder as it says they are already there.
I have almost 25,000 images in my catalogue. I do not want to take the wrong action and loose several years of cataloging and editing.
A search has found similar problems reported for various LR versions going back to LR4, but I cannot find any reported solutions or explanations. Any help or insights would be very much appreciated.
Try creating a new catalog and importing this catalog into it, it may correct the behavior and you won't lose anything (importing from a catalog leaves the catalog intact).
Thanks for the tip. I have done this and it has worked a treat, except for one aspect...
None of my published services have moved across. So whilst it solves the main issue of the catalogue corruption I have lost the links to my images on Flickr and other Hard Drive folders which I publish to for image sharing. This is not the end of the world, but a solution that doesn't loose these connections would be preferable.