I am running some speed tests and having issues with mobile.
In desktop I rank 97 in Google PageSpeed Insights (First Contentful Paint less than a second), but in mobile I only rank 70 and First Contentful Paint is 4,1 seconds
I do use a CDN, caching on the server side (varnish) and using WP Rocket.
For starters, you can try combining your CSS to reduce the number of request.
Consider preloading the page hero’s background image as well.
As for how to do it, you simply hook <link rel="preload" as="image" href="full_url_to_the_image"/> to wp_head of your site. Replace the href with the url path of the image you use as the background of the page hero. 🙂
A wise man once said:
"Have you cleared your cache?"