Hi. I have a similar problem to this.
But it´s weird because i have dozens of HTML articles working. 22 in the same issue.
This particular article http://revistamedicina.net/ojsanm/index.php/Medicina/article/view/1531, doesn´t work. It downloads, not displays the view
I didn´t upgrade OJS recently, everything works fine in other articles. Actually, I tried other HTML articles in this galley and they worked, i checked the code, checked the links, I tried a mixed article, title and references from this article and the body text from another, and it works, but when i copy the “body text” of this problematic article, doesn´t work again. I tried so many things and nothing. Is there something in text (special character or something) that could block the viewing?. The article is simple, not images, not to long. I don´t know why this galley is not recognized as the others.