Hi,
The issue is not the plugin in this case, but an effect called the flash of unstyled content. Viewing the site from a cache-cleared browser looks like this for a second: https://i.imgur.com/ksKgWxA.png
This happens on first page load only, as the second time the browser already cached the assets locally.
The cause of this issue is a CSS lazy loader, which loads your stylesheet files asynchronously upon page load, or places the CSS to footer of the page. In your case, I think this is the Rocket loader feature from Cloudflare, but it can be something else as well – usually cache plugins have an option to include CSS in footer or load the asynchrounously.