Fair enough
Here it is . It's about the #intro h2.xl apparition effect not reverting well while scrubbing (scrolling back up).
https://codepen.io/eZoulou/pen/XWgQJKB
Thanks a lot for the attention.
By the way, as well as I would like to understand the reason of the 'bug', I have found a workaround by using a callback
onLeaveBack: () => {
// Workarround scrub not showing back titles.
gsap.set('h2.screen'+ (i+2), { display : 'block'}, 0.0001);
}