Google Study: LCP Optimization Fails Due to Browser Misidentification

Image credit: Search Engine Journal

SAO PAULO — Google Search Advocate John Mueller recently highlighted a case study from Brazilian e-commerce platform Nuvemshop, which revealed that web performance optimization efforts often fail because browsers incorrectly identify the Largest Contentful Paint (LCP) element, particularly in highly customizable web layouts.

The web.dev case study detailed Nuvemshop’s year-long effort to improve Core Web Vitals, a set of metrics Google uses to assess user experience, finding that misidentification of the LCP element was a primary obstacle to progress.

Nuvemshop discovered that CSS transitions on carousels and banners, alongside issues with lazy loading and image priority, often led browsers to select the wrong LCP element, according to the report.

After implementing three key LCP fixes, Nuvemshop significantly improved its good LCP scores from 57 percent to 96 percent. These fixes included removing CSS transitions from top sections, disabling lazy loading for above-the-fold images, and adding fetchpriority=”high” to potential LCP elements.

The company reported an overall Core Web Vitals pass rate increase from 48 percent to 72 percent following the optimizations. Nuvemshop also observed an 8.9 percent increase in conversion rate for mobile visitors arriving from Google organic search, the study stated.

The case study, also highlighted by Google’s Barry Pollard, emphasized that correctly identifying the true LCP element is important before applying any optimizations, particularly in template-driven or carousel-heavy website designs.

Data from HTTP Archive and research by Deloitte have consistently shown the impact of web performance on user engagement and business outcomes, reinforcing the importance of metrics like LCP.

Source: Search Engine Journal