Database optimizations are not working
Database optimizations require that WP-Cron is triggered reliably on your site.
To check if cron is working for your site in general, please go to Tools > Site Health in your WordPress dashboard and see if any "scheduled events" have failed or are late to run.
Please see our guide about setting up a real cron for your site.
Optimizing a large number of items
This feature uses a background process so the page must be refreshed to see progress.
Transients are not cleaned up
Transients are frequently re-created by plugins. So you may clear the transients but find that it does not reduce to 0. This is normal since plugins are constantly regenerating transients.
To get more information about the created transients, you can install the Transients Manager plugin. The Name column might tell you more about which plugins are creating transients.
Optimize Tables does not work or shows 0 tables to optimize
WP Rocket will not optimize tables if they use InnoDB. If the number of tables optimized is always 0, this is most likely the reason. You can check with your host to confirm if your database uses InnoDB.