How to add a slideshow inside a node with Slick?
The problem comes from an incompatibility from the theme I use, Zircon, with Slick carousel.
The full explanation and the solution can be found here : https://www.drupal.org/node/2875173#comment-12075392

In brief, the solution is to comment the following lines in zircon.libraries.yml with the # sign :

# assets/includes/slick/slick/slick.js: {}
assets/includes/bootstrap/js/bootstrap.js: {}
assets/includes/flexslider/jquery.flexslider.js: {}
assets/includes/flexslider/jquery.flexslider-min.js: {}
assets/js/slideshow.js: {}
# assets/js/carousel.js: {}


This file is in /themes/zircon/ folder