no selection marks on optimization

In the Smart Optimization and Performance section, we have four icons for each page: Images, Cache, CSS, and JavaScript. After performing optimization, I noticed some checkmarks appear.

For example, on the homepage, every icon at the bottom has a checkmark, but on other pages, the Cache and CSS icons do not have checkmarks.

• How can I know (or be sure) that all pages are actually cached?
• I also have the impression that the homepage loads quickly, but other pages are slower.
• How can I check if caching is working on mobile devices as well?

I’m currently using the free version of the plugin, just for testing.