Site doesn't render properly in Instagram browser

Hi,
When my site accessed from the link in an Instagram bio, it does not render correctly. The menu appears broken and the sections with The Grid Elements also do not follow the correct layout. Not sure if it’s a connected issue, but when I use Google’s mobile-friendly test tool the preview of what Google sees also looks like this. Any idea what is causing this?

I have attached a screenshot of how it looks in these instances.

It renders properly in Safari mobile and Chrome mobile browsers.

The site is https://paulstennett.net.

Thank you!

Hello There,

Thanks for writing in! Instagram browser may have blocks some or several JS and CSS files to make your site work properly. Regretfully we do not have any control over this. It is up to instagram to allow or not to allow your site resources to load it up in the browser correctly.

Thank you for your understanding.