Next.js
Published reports for this stack, with severity, affected version, and a direct path into each diagnostic.
Next.js App Router does not emit `<link rel="preload" as="style">` hints before blocking stylesheets in the initial HTML, forcing the browser preload scanner to wait until the parser encounters each `<link rel="stylesheet">`, which delays FCP.
In Next.js 16.3.5 with Turbopack, the web worker bootstrap parses its configuration from the URL hash. In-app browsers like Facebook/Instagram append query parameters (e.g. ?fbclid=abc) after the fragment, making the hash value invalid JSON and causing JSON.parse to throw, preventing worker startup.
When a static route's cache entry passes its `expire` time, Next.js sets `isOnDemandRevalidate = true` for the blocking regeneration. This causes `unstable_cache` to skip reading from the cache entirely, including the prerender resume data cache that was populated during the prospective prerender pass. As a result, the final pass fails with `NEXT_STATIC_GEN_BAILOUT` and returns HTTP 500.
On Vercel deployments, the root route's server-side usePathname() returns "/index" instead of "/", leading to React hydration error #418 and missing SSR output for client components that branch on pathname === "/".
Next.js 16.3.0-preview.5 strips the --max-old-space-size Node flag from build workers when isolatedMemory is true, leaving no memory bound for page-data collection. Large module graphs cause worker SIGKILL, independent of bundler (Turbopack or Webpack).
Next.js Turbopack production build consumes the entire 4 GB container memory when compiling ~12,000 client modules, causing continuous cgroup limit hits and either a kernel OOM kill or a timeout without forward progress. The issue affects 16.3.2 and 16.4.0-canary.4.
When calling notFound() inside a page component in Next.js App Router, the initial server response contains only client-side script tags, not the server-rendered Not Found page HTML. This affects both development and production, including static pages returning incorrect 200 status in production.
When a dynamic new Worker() path is used, Turbopack expands the directory context to include all files, including .d.ts, .d.cts, and .d.mts declaration files, which cannot be loaded at runtime. This leads to 'Unknown module type' or module format mismatch errors and breaks builds.
Using new Worker() with a path derived from import.meta.url in an ESM package under Next.js Turbopack throws 'Cannot find module', even though the worker file exists. The CommonJS version with __dirname works. This is a regression from Next.js 16.0.2.
When using parallel routes inside a route group, calling router.refresh() after a soft navigation can trigger a full-page reload instead of a soft refresh, causing loss of UI state and a broken user experience.
On the WASM SWC bindings, codeFrameColumns deserializes options directly into a strict CodeFrameOptions struct that cannot accept boolean color or undefined maxWidth, unlike the native N-API binding. This causes 100% of code frames to fail on the WASM fallback, replacing the actual error with a serialization error in the dev overlay, server console, and build diagnostics.
Under plain HTTP/1.1 self-hosting, a burst of router prefetch (_rsc) requests occupies all six browser connections per origin; a Server Action submitted while prefetches are in flight is queued/aborted, leaving the UI frozen on stale props. Deterministic reproduction included.
Calling revalidateTag(tag, 'max') after revalidateTag(tag, { expire: 0 }) on the same tag overwrites the earlier immediate expiration, causing stale content to be served instead of a blocking refresh.
In Next.js dev with Turbopack, the HMR WebSocket connection is closed before it is established, causing the first client-side navigation after a fresh page load to delay or fall back to a full page reload. After a manual reload, the connection succeeds and navigation works normally.
When using Next.js 16.4.0 with cacheComponents and a custom cacheHandler that starts empty (e.g. Redis after eviction), a client-side navigation to a prerendered dynamic route (generateStaticParams) returns an unresumable fallback shell instead of rendering the page, causing React error #412. The issue originates from app-page-runtime.js marking non-prefetch RSC requests as static due to the presence of prefetchDataRoute, and then serving the fallback shell on a cache miss instead of dynamically rendering.
sitemap.ts (and robots.ts) that export `revalidate` are incorrectly classified as STATIC_FILE in the adapter build output, losing their revalidate value and causing stale content on Vercel. The route is never regenerated and no function is emitted.
When a dynamic RSC request or form POST resumes a prerendered page with cacheComponents enabled, the literal bracketed URL segment is treated as a fallback route param, and the combination with cached postponed state triggers invariant E592, causing 500 errors.
When using Next.js webpack with PostCSS 8.5.24+ and Sass, a BOM emitted by Sass at the start of each module is preserved in the middle of the concatenated CSS asset. This leading U+FEFF becomes part of the first selector of affected modules, causing those CSS rules to silently fail to match elements. The build succeeds without warnings.
Next.js 16.5.0-canary.3 with `turbopackModuleFragments` enabled panics during build with `ModuleId not found for ident ... [app-client] (ecmascript) <internal part 0>` when a server component references a plain function exported from a 'use client' module that imports another module.
Next.js build tracing with webpack on Windows can fail when a traced dependency computes a home-rooted dynamic path. @vercel/nft then emits a glob whose base directory is the user profile, recursively walking Windows junction cycles (`Application Data` -> `AppData\Local`) and surfacing fatal `EACCES: permission denied, scandir` webpack errors.
When a route segment uses <Suspense fallback={null}> and the content suspends initially, the InnerScrollHandler effect in layout-router.tsx returns early because no client rects are available, preventing the expected scroll-to-top on navigation. The scroll only occurs on a later navigation. A ResizeObserver-based fix ensures the effect reruns once the suspended content lays out.
The default `use cache` handler stores `streamToBuffer` results that may be small slices of a shared Buffer pool slab. Long-lived cache entries therefore retain whole pool slabs (64 KiB on Node 26) while the LRU only counts the slice's bytes, causing actual memory usage to exceed `cacheMaxMemorySize` by up to 22x.
When cacheComponents is enabled, the export worker serializes the entire batch of static pages' resume data caches into a single IPC message, exceeding Node's maximum string length. process.send throws RangeError: Invalid string length, which becomes an unhandledRejection, leaving the parent waiting indefinitely and causing the build to hang at 'Generating static pages'.
Next.js 16.2.0 and later respond with a 500 Internal Server Error when receiving an OPTIONS * request, whereas earlier versions correctly returned 400 Bad Request or another valid response. This regression affects both development and production servers.
Next.js cacheComponents span-creation exemption is applied after instrumentation.register() returns, but @vercel/otel FetchInstrumentation captures a concrete Tracer during register(); subsequent outgoing HTTP requests in prerender create spans through that unpatched tracer and trip the sync-IO guard, producing a Math.random() prerender error.
When a CSS file is imported by both a page and a component loaded with next/dynamic and kept mounted via _app, the stylesheet link is incorrectly marked with data-n-p and removed during client-side navigation. This happens because the dynamic CSS manifest is not loaded correctly in the route module and not passed to _document.
Regression in Next.js 16.0.3: detached-flush child spawned on dev server shutdown hangs after submitting telemetry when next.config leaves a live handle, causing orphaned processes to accumulate and consume large memory/CPU.
When using Next.js 16 with Turbopack (default bundler), importing a native Node addon (built with napi-rs) from a separate package in a pnpm workspace during server-side prerendering results in `TypeError: (void 0) is not a function`. The package is added to `serverExternalPackages`, but Turbopack still bundles or mishandles the native module, causing the imported binding to be undefined.
Manual mocks in Jest are no longer resolved automatically after upgrading to Next.js 13.2.4; the next/jest preset appears to have broken Jest's default __mocks__ lookup.
Next.js App Router client-side Link navigation to a route whose shared layout calls redirect triggers infinite RSC fetch loop; direct destination navigation works. Reproduced on Next 15.1.7 through 16.4.0-canary.57 with both webpack and Turbopack.