Why site failing the Core Web Vitals Assessment?

Topic summary

A Shopify store owner reports their site is now failing the Core Web Vitals Assessment in Google’s PageSpeed testing tool, after previously passing. They’ve shared screenshots showing the failure but are seeking help to:

  • Identify the root cause of the Core Web Vitals failure
  • Understand what specific issues are triggering the failed assessment
  • Find solutions to fix the problems and restore passing scores

The post includes multiple screenshots (currently displaying with formatting issues) that likely show PageSpeed Insights results with failing metrics for Largest Contentful Paint (LCP), First Input Delay (FID), or Cumulative Layout Shift (CLS). No responses or solutions have been provided yet, leaving the issue unresolved and the discussion open for community input.

Summarized with AI on November 8. AI used: claude-sonnet-4-5-20250929.

Recently Page Speed tester has shown Core Web Vitals Assessment as “failed”.

Can anyone tell me what is wrong / causing this, and how to fix it?