[Smush Pro] Missing images in web pages using Smush Pro

Images cannot be loaded in some pages using Smush Pro and the CDN activated.
I.e. in the page:
there are 2 images missing.
One of them ahs this address : https://390982.smushcdn.com/358767/wp-content/uploads/2019/01/Gaetano_Salvioli-1.jpg?size=300×150&lossy=1&strip=1&webp=1

and from this address you get this error:
{“success”:false,”data”:”Error: CWebp was unable to optimise image, result:255 File: \/tmp\/smush_NW3IE8″}

Could you please help me to understand what’s happening? If I disable Smush Pro everything works fine