Map of categories not showing

Love the plugin. Simple to use and does what it should. Only showing the map with Posts in a category does not work.

If I go to /category/[category name]/map/ I would expect a map to display. Unfortunately it’s just an empty page. I though do have some markup that would suggest that there should be a map.

<main id="main" class="site-main" role="main">
<header class="page-header">
<h1 class="page-title">Kategorie: Petermobil</h1> </header>
<img class="archive-map sloc-map" src="" />
<ul>
</ul>
</main>

I’m using Google Maps. The rest works just fine.