Services

Fix Next.js Core Web Vitals Regressions After Launch or Release

You are in the right place when the stack was performing acceptably and then got slower after a release, redesign, dependency change, or new third‑party load.

Recover lost Core Web Vitals after a release before the site feels slower and key routes start hurting conversion, crawl efficiency, or release confidence.

Typical symptoms

  • Largest Contentful Paint, Interaction to Next Paint, or CLS worsened after a release.
  • The site still works functionally, but user‑perceived speed has clearly degraded.
  • The regression is being discussed in dashboards but the cause is still unclear.

Likely causes

  • Rendering strategy, assets, or script changes increased work on critical routes.
  • Caching or data‑fetching behaviour changed in a way that slowed the page shell.
  • Third‑party additions or component regressions are affecting live traffic.

What I look at first

  • Quick check: identify which routes and which metric moved first in field data, not just in lab traces.
  • Recent rendering, asset, or dependency changes on critical page types.
  • Whether the regression is primarily network, render, or scripting driven.

How I help fix this

  • Isolate the regression to the smallest credible set of technical causes.
  • Define the fixes that deliver the largest measured improvement first.
  • Support remediation and verify that the regression really moved back down.

When to bring me in

  • Bring me in when the regression is visible in live traffic but the root cause is still unclear.
  • Bring me in when dashboards show the problem and releases are still piling more change on top.

Related project experience

  1. Nando’s

    Senior software engineer on the UK and Ireland replatform, migrating Nando’s customer‑facing websites from legacy Drupal to a unified headless platform built with Next.js and Storyblok, with a focus on performance, accessibility, and SEO.

    Screenshot of the Nando’s website; part of John Kavanagh's development portfolio.

  2. Selfridges

    Lead front‑end developer within the e‑commerce Customer Experience team. Leading the delivery of new features, as well as considerable refactoring and improvement of the existing platform's performance.

    Screenshot of the Selfridges website; part of John Kavanagh's development portfolio.

  3. John Lewis
    & Partners

    Senior developer as part of team 'Findability'. Led the digital implementation of the 'John Lewis & Partners' rebrand alongside new feature development, user journey optimisation, and performance improvements.

    Screenshot of the John Lewis website; part of John Kavanagh's development portfolio.

Supporting technical articles

Related services

  1. Parent hub

    Next.js Performance and Stability

    Choose the right performance and stability investigation when a live Next.js stack is slower, less stable, or harder to reason about after change.

  3. Adjacent scenario

    Next.js Hydration Mismatch Fix

    Diagnose hydration mismatches before Hydration failed errors, brittle UI, and production‑only rendering bugs start compounding.

Tell me what needs fixing

Send me the affected page or route, point me at the code if that helps, and tell me what you expected to happen versus what is happening now. If this connects to a Next.js migration, technical SEO drop, performance issue, launch, or platform move, include that context too. I'll come back with the clearest next step.

Send the details
Skip past clients

Previous Clients