Well for some reason, HTML files that are in a resources folder get lost along the way.
A file like content/posts/post_1/resources/myfile.html won’t be accessible via http://mysite.com/posts/post_1/resources/myfile.html.
The same file renamed to content/posts/post_1/resources/myfile.txt will, however, be accessible through http://mysite.com/posts/post_1/resources/myfile.txt.
I guess that somehow Hugo filters out HTML files that are inside a resources folder.