Animate text as the user scrolls over a sticky positioned div

I am trying to animate four headings as the user scrolls. First I create a sticky positioned div, then the user scrolls over the headings toggling the class .active one at a time, leaving the last one visible and continuing scrolling to the last div.

The problem I am having is that once the .sticky div becomes sticky the browser no longer detects further scrolling until the div becomes non-sticky again.

--- UPDATE

I have changed the code to transition sequentially and works better, but I would like to start the animations only when the .sticky div becomes sticky, but I tried that and the scroll animation stops working completely. Also, I would like to keep all headings on the same block but If I do position: absolute on them it breaks the animations too.

const headings = Array.from(document.querySelectorAll('.animated-text'));
const sticky = document.querySelector('.sticky');

let currentActive = null;

window.addEventListener('scroll', () => {
  const viewportHeight = window.innerHeight;
  headings.forEach((heading, index) => {
    const headingRect = heading.getBoundingClientRect();

    if (headingRect.top <= viewportHeight / 2) {
      if (currentActive) {
        currentActive.classList.remove('active');
      }
      heading.classList.add('active');
      currentActive = heading;
    }
  });
});

body {
  margin: 0
}

section {
  position: relative;
}

.sticky {
  padding-bottom: 150px;
  background: #2d232c;
  position: sticky;
  top: 0;
  overflow: hidden;
  height: auto;
  color: white;
}

.animated-text {
  opacity: 0;
  height: 0;
  overflow: hidden;
  transition: opacity 1s ease, height 1s ease, transform 1s ease;
  transform: translateY(0);
}

.animated-text.active {
  height: auto;
  opacity: 1;
  transform: translateY(-20px);
}

.hero, .end {
  height: 100px;
  background: white;
}

<section class='hero'>
  <p>Start</p>
</section>

<section class='sticky'>
  <div class='text-animations'>
    <h1 class='animated-text active'>Intro</h1>
    <h2 class='animated-text'>First</h2>
    <h2 class='animated-text'>Second</h2>
    <h2 class='animated-text'>Third</h2>
  </div>
  <p class='intro_content'>
     Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam
  </p>  
</section>

<section class='end'>
  <p>End<p>
</section>

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