Accessing site elements appear (chronologically) in random order

Hi friends,
I’ve build a WP site with Eightdegree template.
On the first position (on the top) I’ve the main menu, and just below, the slider (flexslider by woothemes.com), and below again, other images ad text…

Now happen this: when the site are loading, first appear (in chronological order) the underlying pictures, then after a few seconds the menu and in the last the flexslider. Then, after few seconds everything is right.

I have also reduced the weight of the images but the problem remains.

How I could debug this kind of problem?

many many thanks

Davide