As my title explain it, i used to activate minify function in W3TC , combined manual set up for css an js, listing every scripts in the correct parts of my page (<head>, <body>, </body>)
My website ran like this for months, then i ran several web page speed tests, and i discovered that the minify combined files had a very long waiting time for first byte. It's strange cause these files are not supposed to be generated "on the fly"... (not sure of this). So i just disabled minify function W3TC, and yes i have really too many css and js files, but the loading times are really better... (about 1 second in every tests i did.
What could explain that strange issue ?
I d'ont know, but i'm going to manually deregister styles and scripts, and manually load the combined files.
So to every user of w3tc, you should try this yourself, because 1 second is not nothing ;)