If when you run the duplicate search Lightroom shows an error message complaining about 'fileAttributesAtPath' or 'rootFile', it's a strong indicator of a corrupt catalog.

As a test, try running the search without the "Filename" option. If there is a problem in the catalog with filenames, then the error would appear when the plugin requests full filename details for photos. This may allow the search to finish, but would still leave the problem in the catalog. It isn't anything to do with files being offline or unavailable, it's a problem with the way that the filename is stored inside Lightroom's internal database.

If the catalog is damaged then there are a few options. The fastest would be to just export the entire catalog to a new catalog (File->Export as Catalog...) and use that from now on. That may work, depending on the type of problem. If that doesn't help then you would need to find the photo that's causing the problem, remove it from the catalog and re-import it. The fastest way to do this is to run the plugin on half your catalog and, if you still have the error, half of that and so on until you find the exact photo. There may be more than one.

The reason that this error is triggered by the duplicate finder is that it needs to access a lot of data about all your photos. Lightroom itself is unlikely to show a problem unless you actually select the damaged photos, and maybe even not then.