HTML files in static

I have some html slides created with R Markdown that I want to link from a blog post to be displayed in-browser. I have put them in static/slides. When I use the serve_site() function from the blogdown package in R everything works as I would like. However, when I commit my site to be rendered by Netlify the file does not display correctly in browser (see http://eddjberry.netlify.com/slides/intro_to_r#1). However, the file is clearly ‘there’, as can be seeing by viewing the page source.

I’ve had a look through posts and documentation on this issue and everyone says that files in static are copied over without modification. However, there seems to be some modification going on here. I wasn’t sure whether it was an issue with Netlify itself? When i commit to GitHub the build command is hugo and the hugo version is 0.24.1. I realise that if it’s a Netlify issue then it’s not for this forum.

For further information on what I’m trying to achieve (if it isn’t clear) you can see the second half of this page in the book about the blogdown package (https://bookdown.org/yihui/blogdown/static-files.html), which includes a link to an example site.