Hello,

In the WP Rocket settings, you have enabled the “Remove unused CSS” option. The “Remove unused CSS” option doesn’t work in most cases and does not load necessary styles https://gyazo.com/59d2121eb6daf879839376b3646db615
Unfortunately, we don’t have a list of selectors to fix this since it is always individual for most of the websites.
You can either disable it or contact WP Rocket for help.

So after disabling it and clearing the cache, the product gallery on the product page started to work well.

Kind Regards