If the search bar uses a monospace font, or the search input and dropdown filters are all placed on separate lines, then there is probably a pre or code tag wrapped around the [wpsl] shortcode in the text editor.

You can check this by opening the page that contains the [wpsl] shortcode in the editor, switching to text mode and checking to see if there are any tags wrapped around it. If this is the case, remove them and save the page.