@juliendntfr: Hello Julien,
Go to => Appearance => Customize => Additional CSS and add the following CSS Code.
@media screen and (max-width: 600px) {
.tiled-gallery-item.calling-this img {
width: unset !important;
height: unset !important;
}
}
Let me know if this works out!
Kind Regards,
Skandha