GTMetrix says “Serve resources from consistent URL”

1. It’s not a big deal. Seriously.

2. Do you have any security plugins that might be removing version information from your site?

Steven,
Thank you for your encouraging comment!
1. I am mainly concerned because my site is very slow at loading the first page and I am suspecting that this large CSS file loading twice could be the culprit…

2. I can not figure out if one of my plugins could be involved . Here is the exhaustive list of the plugins I am using :
Arconix FAQ
Contact Form 7
CPO Companion
Custom Sidebars
Duplicate Post
Flamingo
Hummingbird
Simple Calendar
Simple Custom CSS
SiteOrigin Widgets Bundle
TablePress
UpdraftPlus – Sauvegarde/Restauration
WP DB Booster
WP Google Maps
WP-Optimize
WPFront Scroll Top (inactive)
YouTube widget responsive

The speed of your site has nothing to do with the CSS file. You have a 1.4 second TTFB (time to first byte). That plus the large image account for most of the time to serve your site.

The TTFB issue is usually addressed by caching. Are you using any caching plugins? My typical recommendation is to use these two plugins: autoptimize and comet cache.

Since you’re already using Hummingbird, I recommend asking at https://www.ads-software.com/support/plugin/hummingbird-performance#new-post so the plugin’s developers and support community can help you with this.

As you’re using Cloudflare, too, you might check with their support to see why the TTFB is so high.

Thank you for eliminating the CSS possibility of slowing down my serving of the first page and to clarifying the TTFB issue.

Indeed, I am both using Hummingbird and Cloudflare and at some time I was using caching plugins as well.

Recently I tried to turn off all of caching plugins since Hummingbird was giving me the following message :

Hummingbird detected an advanced-cache.php file in wp-content directory. Please disable any other caching plugins on order to use Page Caching. Unfortunately, I have no idea how to deal with this “advanced-cache.php file” and how to turn it off….

I understand that I should now switch to the Hummingbird and/or Cloudflare forum sections to investigate my long TTFB issue?

yes

OK Steven
Thanks a lot,
Jacques