Thank you very much for your support.
I found an easy solution.
First of all I excluded Picu from the cache as you suggested, but this solution didn’t work.
So I modified the file “piculight.css” inserting the value height:0px instead of 70px to the .picu-lightbox-navigation class.
Now viewing individual photos looks good.
Remains to adjust the bottom menu because you see everything moved to the left and not understand it well.
Here is the example page with the problem partially solved:
https://www.photoidea.it/raccolte/98ba6/
Thanks again for your help.
Daniel