In _document.tsx file, we've got a favicon loaded. This is visible in the code below. It works on most pages, but once they get a certain depth they stop working. The short version is that it works for normal pages and archive pages, but not single pages. Looking for a reason, so it can be fixed.
// imports
import { Head } from 'next/document';
// component
<Head>
<link rel='icon' href='img/favicon.ico' />
</Head>