The problem was with my JS files optimization, I fixed it, thanks.
Last question by the way.
Under Best Practices, I have this user experience warning: Low resolution images
For optimal image clarity, the natural dimensions of the image should be proportional to the display size and pixel rate.
Displayed size: 220 x 54
Actual size: 220 x 54
Expected size: 440 x 108
Do I have to put the logo in 440 x 108 ?
Or put a SVG logo instead of the PNG logo ?