WP Rocket issue – WP fastest Cache

I got 2 webistes. One I decided to download WP fastest Cache Premium, works a DREAM! On the other one, my colleague insisted on WP rocket, also the premium version. He is ill at present and I am struggling with this plugin. I am sure it’s good also but it’s not that straightforward. When deferring javascript you can see the image on the homepage still but it doesn’t load beyond the blur. There is obviously a JS I need to exclude for this to work but I don’t know where to start. The trouble is their support is set up with his email which I cannot access either. Anyone got any tips? Thank you.