Ok, after many tries I think I’ve found a solution, I’m not sure if it’s the final solution, but it seems to works.
The problem is a possible css declaration relative to the img tag. In my case I’ve this css style that breaks the map:
.entry-content img {
max-width:100%;
}
The solution is to ovveride the style using, for example this declaration:
.acf-map img {
max-width:inherit !important;
}
Please try and let me know if it works for you. Thanks in advance.