Simple iframe of html file results in infinite loop of index.html in preview

Hi all,

I want to embed an html file (folium.html) using an iframe. But for some reason, if I want to preview the site, the iframe infinitely loops index.html. Minimum working example of custom code section in <body> below. When I export the code and manually open index.html, it does work as expected. Why? It would be nice to be able to use the preview functionality.

<div>Website title</div>
<div><iframe src="./folium.html"></iframe></div>

Result: Screenshot of minimum working example