this article [...]font-awesome-does-not-display-when-using-cdn.html Pretty much spot on!

In short, your addition of CDN has set off a security warning, that by default, is blocked. The resolution in the article worked for me.

Add the following to the site's root '.htaccess' file.

<IfModule mod_headers.c>
     <FilesMatch "\.(ttf|ttc|otf|eot|woff|font.css)$">
          Header set Access-Control-Allow-Origin "*"
     </FilesMatch>
</IfModule>
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