Hi there,
Seems that you’re enabling Default editor which often strips some HTML tags in content. That’s why you can only see above <div>.
Kindly go to Backend > Global Configuration > set ‘Default Editor’ to ‘Editor – None’. Then you go to backend settings of this module again, you should see output content like this:
<!-- AddThis Follow BEGIN -->
<div class="addthis_toolbox">
<a class="addthis_button_facebook_follow" addthis:userid="joomlart"><i class="fa fa-facebook"></i></a>
<a class="addthis_button_twitter_follow" addthis:userid="JoomlArt"><i class="fa fa-twitter"></i></a>
<a class="addthis_button_rss_follow" addthis:userid="joomla.org/rss.html"><i class="fa fa-rss"></i></a>
</div>
<script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#pubid=ra-523d4894767843b5"></script>
<!-- AddThis Follow END -->