After deleting a photo in Preview it still appears in the thumbnails

MacBook Pro (2 GHz Quad-Core Intel Core i5); Sequoia 15.1.1

Have just updated to Sequoia. After opening several photos in Preview, when I delete one (ie. Move to Bin) it still appears in the thumbnails, and another of the opened photos appears at the bottom of the thumbnails (ie. not the one I deleted) without a filename. If more are deleted, more different photo thumbnails appear at the bottom of the lhs. Clicking on a thumbnail without a filename does nothing. Clicking on a thumbnail with a filename (after deleting a photo) sometimes brings up a different photo.