Views Rewrite return html string instead of rendering them
I think it could be because of the &lt;i&gt;....&lt;/i&gt; tags part, if you take that out, does it render? Seems like views uses Filter HTML, and only popular html tags are allowed on Custom Fields or Re-Write boxes.

You should be able to achieve your goal by creating a template file.

views-view-fields--[view-name]--[machine-name].html.twig

&lt;span class="stats"&gt;{{ fields.totalcount.content }}&lt;i aria-hidden="true" class="fa fa-eye"&gt;&lt;/i&gt;&lt;/span&gt;