Website performance gone down after cloudflare cdn activated

I wanted to checkout Cloudlfare CDN free version for old website and activate CDN for it and noticed that Website performance was hit after activating the CDN. What could be the reason as I am new to Cloudflare CDN. Our Website is an old website and hosted in dedicated server.

here is my screenshot of GTMetrix :

CDN was activated and you can see test run on GTMetrix 15 days back show website much faster than what its is showing since yesterday…

Any advice what could have gone wrong?