I just tested this on a basic WP site with nothing else installed. If I add this to the main editor in code view.
<div itemscope itemtype="http://schema.org/Review">
<meta itemprop="description" content="Skylight Alternative. Fill your home with the sun's free natural light." />
<meta itemprop="datePublished" content="2016-08-15" />
</div>
the switch to visual and then back to code view, the only thing that’s still there is
<div></div>
So I have to assume that you have something already installed that is modifying the main WP editor field.