Please refer this article Adobe Lightroom - Find moved or missing files and folders and ensure you are following the correct approach of relinking Files/Folders in Lightroom.
Thanks for the link Akash,
Unfortunately I know how to find and restore images, my problem is Lightroom doesn't even seem to be able to see that there are images within the folder in this instance and doesn't seem to know where any of the >5K images I've worked on recently are. See the images below, the folder in Lightroom says 0 images, yet you can see in finder that there are hundreds in that folder.
I can go through the whole reimport proceedure, see all the images in finder as i progress, click import and it takes it's time like it's importing the images then I get this:
I'm pretty alarmed to think that the hundreds of hours spent processing images in the past can be lost like this. Professionally I cannot afford this sort of unreliability.
Something is wrong with your external RAID drive. LR can't connect to it. That is why there is a question mark on the folder for it at the top of the Folders list in the Library module.
Your symptoms indicate that the photos are in Lightroom, but (probably accidentally) are no longer in the folder you think they were in, Lightroom thinks they are in a different folder. If that's the case, then you will not be able to import the photos again (and you don't want to import them again anyway). You need to find them in Lightroom.
Click on All Photographs, turn off filters (looks like they were off in your screen capture), expand all stacks, and then use the Filter Bar to search for at least one of these photos by file name.
Also please note that you have a 2014 folder with a question mark on it in Lightroom that has 123 photos in it, which probably is the reason why the photos cannot be found by Lightroom at this time.