Not showing Thumbnails Adobe Apple Photoshop why doesn’t this work can anyone fix

Mac computer not connecting Adobe thumbnails rename backspace then I see files.. I can rename files undo then the images will show up. Large Photoshop multi layer doesn’t show up on thumbnail on external drive all types of files fonts I can’t see. El captain it worked fine when I updated to Sierra stop showing thumbnails show up on thumbnail on external drive all types of files El captain it worked fine when I updated to Sierra stop showing thumbnails