Affected version
Reports that share this version, grouped in one feed.
Next.js 16.4+ strict route matching incorrectly treats a parallel slot catch-all from one route group as part of routes in sibling groups, causing valid pages to be reported as unmatched and failing dev/production webpack builds.
When a client component inside a Suspense boundary uses synchronous IO (e.g., Math.random or Date.now) during server rendering, the resumed segment omits the host elements rendered before the sync IO call. This causes a hydration mismatch (React error #418) and the boundary's fallback is replaced with an incomplete subtree.
In Next.js 16.4.0 dev with Turbopack, Pages Router pages crash during hydration because required client modules are not included in any chunk. The regression was introduced by #97664, which seeded availability info from the _app chunk group into page chunk groups; in dev each entry has its own module graph, so availability items from _app are wrongly treated as already available, causing modules like a-page-only and b-boundary to be skipped.
On cold load with a delayed client component chunk, Next.js App Router repeatedly retries root hydration causing thousands of empty commits and significant main thread time. The issue is triggered by `useDeferredValue` calls in `Head` and `InnerLayoutRouter` that pass the current RSC value as the initial value even when no prefetch data exists during initial hydration. This leads to React scheduling deferred work that commits an empty tree, making hydration eligible to retry in a loop.
When a page calls notFound(), Next.js serves a minimal error shell (`__next_error__`) in the server HTML, omitting the root layout, `<html lang>` attribute, and the nearest not-found UI. This breaks accessibility, no-JS clients, and dynamic root layouts, and is inconsistent with the hydrated result. Affects App Router across multiple Next.js versions.