Very low google speedtest result with plugin active

Hi @vincentdb,
This plugin is about page caching both at CDN & disk-level. This plugin itself cannot increase your PSI score massively. As PSI core is not about just your TTFB or how fast your page is being provided via CDN/Server. It is about how your website is designed and contents are laid out.

I would highly recommend you to read the following resources to understand those metrics more clearly:
https://web.dev/first-contentful-paint/
https://web.dev/interactive/
https://web.dev/speed-index/
https://web.dev/lighthouse-total-blocking-time/
https://web.dev/lcp/
https://web.dev/optimize-cls/

All of these matters are depends on how your site is designed. How the CSS are manipulating your pages, how much JS is blocking rendering and taking how much times.

With this plugin enabled your Initial server response time will always be very low as pages are being served either from Cloudflare CDN or from the disk-level fallback cache.
Screenshot: https://i.imgur.com/1J5dxcy.png

Consider taking a deep dive into your website code and seeing which code is doing what and how to eliminate/optimize problematic items codes in order to increase PSI. PSI score is simply not a speed test of your website and how much faster your site is loading.

For that, you should check: https://www.uptrends.com/tools/cdn-performance-check?toolRequestGuid=ae82c37b-56ec-4633-8294-e6e13ca7c97d

Thanks for the super fast and complete answer. Great!!