odd behavior: image placeholder shown instead of pages

[Jaguaro]

Hi, my website www.fateicapricci.it has been a quite odd behavior lately: 

- sometimes it shows image placeholder instead of pages, categories, etc.

- sometimes it shows the pages correctly

 

This behavior began when I tried to activate the smarty cache (instead of “force compile”).

Now I'm using again “force compile” and I've cleared the cache (I have no boost performance option set).

I also cleared the browser's cache but the situation haven't changed.

 

What do you think? How could I fix this very annoying problem (which actually risks to compromise completely the navigation on the website)?

 

Thanks in advance

 

C