Recalculate scrolling div position when used in a clipping path

let logos, logoHeight, barTopMargin;
let viewportHeight;

window.addEventListener('load', init);
window.addEventListener('resize', setSizes);
document.addEventListener('scroll', update);


function init(lockUpdate) {
    logos = document.querySelectorAll('.scroll-text');
    setSizes(lockUpdate);
}

function update() {
    // ensure initialization and prevent recursive call
    if (!logos) init(true);
    //*************************************************

    /**************************************************
        THIS LINE MUST BE HERE.
    **************************************************/
    let maxScrollDist  = document.documentElement.scrollHeight - viewportHeight;
    //*************************************************

    let currentScrollPos = document.documentElement.scrollTop;
    let newTop;

    let middle = currentScrollPos + viewportHeight/2;
    let middleY = maxScrollDist/2;

    if (middle >= (maxScrollDist+viewportHeight)/2) {
        let p = (middleY - Math.floor(middle - (maxScrollDist+viewportHeight)/2))*100/middleY;

        newTop = viewportHeight/2 - logoHeight/2;
        newTop += (100-p)*(viewportHeight/2)/100;
        newTop -= (100-p)*(barTopMargin +logoHeight/2)/100;
        newTop = Math.max(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    } else {
        let p = (middleY - Math.floor(-middle + (maxScrollDist+viewportHeight)/2))*100/middleY;
        newTop = barTopMargin*(100-p)/100+(viewportHeight/2 - (logoHeight/2)*p/100 )*p/100;
        newTop = Math.min(newTop, viewportHeight/2 - logoHeight/2); /*fix*/
    }

    logos.forEach(function(el) {
        el.style.top = newTop + "px";
    });
}

function setSizes(lockUpdate) {
    logoHeight     = logos[0].offsetHeight;
    barTopMargin   = parseInt(getComputedStyle(document.querySelector('#page'), '::before').top);
    viewportHeight = window.innerHeight;
    if (lockUpdate === true) return;
    update();
}

updated and tested.

to check it put this code in your console:

document.removeEventListener('scroll', update);
document.onscroll = function() {
    let _logoHeight     = logos[0].offsetHeight;
    let _barTopMargin   = parseInt(getComputedStyle(document.querySelector('#page'), '::before').top);
    let _viewportHeight = window.innerHeight;
    let _maxScrollDist  = document.documentElement.scrollHeight - _viewportHeight;

    let currentScrollPos = document.documentElement.scrollTop;
    let percent100 = currentScrollPos + _viewportHeight;

    let scrolledPercent = currentScrollPos * 100/_maxScrollDist;

    let newTop = ((_viewportHeight - _logoHeight/2)*scrolledPercent/100);

    let middle = currentScrollPos + _viewportHeight/2;
    let middleY = _maxScrollDist/2; // 100

    if (middle >= (_maxScrollDist+_viewportHeight)/2) {
        let y1 = middleY - Math.floor(middle - (_maxScrollDist+_viewportHeight)/2);
        let p = y1*100/middleY;

        newTop = _viewportHeight/2 - _logoHeight/2;
        newTop += (100-p)*(_viewportHeight/2)/100;
        newTop -= (100-p)*(30 +_logoHeight/2)/100;

        newTop = Math.max(newTop, _viewportHeight/2 - _logoHeight/2); /*fix*/

    } else {
        let y2 = middleY - Math.floor(-middle + (_maxScrollDist+_viewportHeight)/2);
        let p = y2*100/middleY;
        newTop = 30*(100-p)/100+(_viewportHeight/2 - (_logoHeight/2)*p/100 )*p/100;

        newTop = Math.min(newTop, _viewportHeight/2 - _logoHeight/2); /*fix*/
    }

    logos.forEach(function(el) {
        el.style.top = newTop + "px";
    });
}

---

CSS fix: custom.css :: line 767

@media (max-width: 1000px)...
.scroll-text {
    padding-left: 13px;
    /*width: 27px;*/
}
.scroll-text img {
    /* remove it. but if necessary move it to .scroll-text rule above
    width: 27px; */
}

custom.css :: line 839

@media (max-width: 599px)...
.logo-scroll {
    /*display: none; why! remove it*/
}

custom.css :: line 268

.scroll-text {
    position: fixed;
    /* height: 280px; remove it*/
    padding-left: 20px;
}

see this capture

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finally, have a nice day and goodby.