Hello, Anshu,
There are no perfect universal settings that would work for all cases, so it is necessary to personally check the options and test their effectiveness and various combinations.
Regarding what you have written – the logic is that if you enable the “Remove Unused CSS” and “AJAX” options in WP-Rocket, it will detect that the style is not needed to be loaded as the element it is associated with does not exist on the page, thus resulting in broken styles.
You need to decide for yourself what is more important to you – a good rating from a test service or the reality that shows everything in a good light. Site testers are just code that tests for the cases that are written for it, so it is best to test your site from your real devices and adjust for your ratings.
Kind Regards,
8theme team