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I'm trying to improve my site's PageSpeed. So far so good, I received score of 91 points for mobile and 97 points for desktops using Google PageSpeed Insights.

However, when I add a CDN service for CSS, JavaScript, and images, the mobile score drops to 79 while the desktop score remains at 97 points.

My question is: Why am I receiving a lower core when using a CDN? There are no additional warnings in the Google PageSpeed Insights report page, just that the mobile score drops by 12 points.

I'm using W3TC/MaxCDN pull zone with default settings.

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Google also tells the errors to fix after the pagespeed score. Look at the suggestions before and after enabling the CDN and see what is getting added up. –  Rana Prathap Jan 8 at 11:52
    
There is no additional suggestions. 8 Passed Rules and only "css blocking" –  Tihomir Jan 8 at 12:07

2 Answers 2

That's probably because the CDN set a cookie and now your images/JS/CSS aren't hosted on a cookieless domain anymore. I found CDN's very useful for traffic intensive sites, but if you're hosting a small site with not that many users, I wouldn't use one.

For my site, the actual page speed (not the score) rose a bit, but my traffic went down by 90%.

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Look at the name of the CSS resource that was "render blocking above the fold content".

If that resource is native to your site, then what happened is the CDN loaded the cached CSS in the initial part of the page that was originally not render blocking above the fold content. There is nothing really useful that you can do in this regard. If there is a specific URL for your mobile sites, you can add a page rule and prevent caching of content for mobile pages. Use tools such as Pingdom Speedtest and check if there is any considerable increase in speed on using the CDN. If not, I would recommend disabling it.

If the CSS file is not a resource of your server(highly unlikely), then purge the cache and try again.

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