⚡ Quick Fix (TL;DR)

The Fix: 1. Check whether `max-height` uses `100vh` — replace with `dvh`.
2. Check whether any `scroll` event listener closes or hides the widget.
3. Check whether the popup has `position: fixed` — if not, it may reposition unexpectedly when the viewport shifts.
Two fixes applied together:

**Fix 1 — Replace `vh` with `dvh`:**
```css
@media (max-width: 600px) {
  .widget-popup {
    max-height: 70dvh;
    position: fixed;
  }
}
```

**Fix 2 — Guard the scroll listener:**
```javascript
window.addEventListener('scroll', function() {
  if (popup.classList.contains('open')) return; // ignore scroll while widget is open
  // hide launcher logic...
});
```