Book- and/or Site-Tile missing on all pages

On a rendered book there is no title - neither of the book nor of the page on the top of the page

(See screenshot)

An empty <h2>-Tag is rendered - so I assume it is just a bug that this is missing.

I would assume that there are one of the following

<h1>[book-title]</h1>
<h2>[page.title]</h2>

or

<h2>[book-title] - [page title]

or <h2>[page title]</h2>

Currently we are in need to repeat the page title as a section name at the top of the page - which leads to (optical) duplicate entries in the structure