React app crashing in production.Fixed in 4 hours.

PM assigned in 10 minutes. React engineer starts diagnosing within the hour using your Sentry error reports and Vercel or Netlify function logs. React white screens in production have a small number of root causes: an uncaught JavaScript exception during component rendering not caught by an error boundary, a hydration mismatch between server-rendered HTML and client React rendering causing React to abandon the entire render tree, a dynamic import failing in production due to a module resolution issue that does not appear in development, or a missing environment variable causing a critical data fetch to return null, triggering a downstream null reference error. The engineer traces the error to the exact component, implements the fix, adds an error boundary to contain future failures, and verifies on the staging URL before production deployment.

Next.js App Router migration issues are one of the most common React requests. The engineer handles: Pages Router to App Router restructuring (converting getServerSideProps and getStaticProps to Server Components with async data fetching), client-component boundary errors from using hooks in Server Components, Metadata API migration from the next/head approach, route handler syntax changes (GET and POST exports instead of default export), third-party library incompatibilities with App Router Server Components (libraries that use context providers in ways that break in the server rendering environment), and the new caching behaviour where fetch calls are cached by default requiring explicit cache: no-store for dynamic data. PM scopes the migration complexity in the first 15 minutes and gives you a realistic fix timeline before work starts.

Yes. Error boundary implementation is a standard reliability deliverable for every React crash engagement. The engineer adds boundaries at the correct granularity wrapping individual page sections and key interactive components rather than the entire application in one boundary (which gives the same white screen). Each error boundary renders a user-friendly fallback UI specific to the component: a data table showing Unable to load data, try refreshing rather than a blank space, a product listing showing some products unavailable rather than an empty page. The engineer also adds error reporting in each boundary componentDidCatch method so Sentry or your error tracker receives the component stack and specific error from production boundaries, giving you visibility into which sections are failing and how frequently.

Third-party library crashes are handled differently depending on whether a patch exists. If the library has released a fix: update the dependency, verify the update resolves the crash, run your test suite to confirm no regressions from the update, and deploy. If no patch exists: implement a workaround wrapping the third-party component in an error boundary to contain the crash, patching the library locally using patch-package (applies diffs to node_modules and persists them across installs), or replacing the library with a stable alternative providing the same functionality. For widely used libraries (Recharts, React DnD, TanStack Query), PM checks the GitHub issues for the exact crash report and links you to the upstream fix timeline so you can plan the permanent resolution alongside the immediate workaround.

Five most common root causes in production: first, calling a method on null or undefined (TypeError: Cannot read properties of null) in a component receiving data from an API where the API returns null in an unexpected case not covered in testing; second, hydration mismatches between server-rendered HTML and client React caused by using window, Math.random, or Date in components that render server-side; third, a dynamic import failing in production because the module path uses a process.env variable not set in the production build; fourth, an uncaught promise rejection in a useEffect or event handler causing React to unmount the component tree; fifth, a stale closure in a useEffect dependency array causing the effect to use outdated data and overwrite state in a way that breaks the render cycle.