Scroll Reset Regression With Parallel Routes And Fixed-Position Slots Due To AppNewScrollHandler Default Change In Next.Js 16.3.0

The new scroll handler (InnerScrollHandlerNew) lacks the shouldSkipElement check that the old handler (InnerScrollHandlerOld) used to skip fixed/sticky positioned elements. When a parallel route slot renders only a fixed header, the Fragment ref passed to getScrollTargetState returns a small positive elementTop, causing initialTargetState to always be 1 ('already in viewport'). The handler then marks the shared scrollRef as handled and returns without scrolling, so the actual content slot never gets a chance to scroll.

1. Create a Next.js app with a parallel route slot (@header) that renders only a position: fixed element, e.g. <header className="fixed top-2">...</header> in @header/page.tsx. 2. Run pnpm dev, open the home page, scroll down about 2000px. 3. Click a <Link> to another page (e.g. /about). 4. Observe that the new page opens at the previous scroll offset instead of resetting to top.

The fix may affect other navigation scenarios where a slot contains both fixed and normal elements; regression testing is recommended for all parallel routes and scroll behavior. If issues arise, the temporary workaround is to set experimental.appNewScrollHandler: false in next.config.ts. For rollback, revert this code change and restore the previous behavior.