If you enable header titles for Posts or Pages etc. you get multiple h1 on the pages. The second h1 gets hidden by css statement display:none. This works for users but not for SEO. Both h1 (which are the same) are used by google which has a bad effect on SEO.
Instead of hiding the second h1 by CSS I would recommend to only place the title if the function kahuna_header_title_check() is false: