Grande Template - Parallax background in mobile

my div "client-testimonial parallax" in homepage, on iPhone 6s and iPad Pro shows no background image, only a background color. If I do a simulation of the mobile view on my desktop computer I see the picture (as it should be).
Did I do something wrong?

Hi Fast max.
Please give me an image that show the problem
I will check it gain.
Thanks you

www.evernote.com/l/APqB4K5VGyFIo5Ugd8DafJ_4hKeJuUxrh8E

Same issue on iPad pro

I'm forced to hide the parallax in Mobile