On your demo page there is a page showing tagged items:
demo.smartaddons.com/templates/joomla3/sj-plus/index.php/joomla-pages/tags/tagged-items
When I create a menu that shows my tagged items, I can only make the image and link to the item show up, but not the description
Btw: description shows up with beez default template.
Edit: Solved: In templates/sj_plus/html/com_tags/tag/default_items.php line 121 change:
<?php if ($this->params->get('all_tags_show_tag_descripion', 1)) : ?>
to
<?php if ($this->params->get('all_tags_show_item_descripion', 1)) : ?>
Then it works. Looks like a bug in the template code