This behavior is caused by the style that you've assigned to the link targets:
Code:
<h2 class="hide" id="sigil_toc_id_13">Absenz</h2>
Code:
.hide {display:none;}
Basically, you've created links to invisibe = non-existing targets.
You might want to change this to:
from:
Code:
<h2 class="hide" id="sigil_toc_id_13">Absenz</h2>
<p><strong>Absenz</strong> · Abwesenheit · Defizit · Fehlen</p>
to:
Code:
<p id="sigil_toc_id_13"><strong>Absenz</strong> · Abwesenheit · Defizit · Fehlen</p>