I have several folders on a external drive. When I expand the folder list the Root Drive shows the location unknown ? even though all sub folders are found. Using Lightroom Classic CC 7.1 I have tried to do reorg and clean up but still folders wont update.
Alt/Option click on the TOP folder, select "Update folder Location". Don't move folders, files, ANYTHING outside of Lightroom or this will happen. Move them from within LR, then it 'knows' what you've done with said files and folders.