Reference: the 5 most common CLS killers — and the fixes

Ranked by observed frequency:

1. Images and embeds without explicit width/height or aspect-ratio — browser allocates wrong space, then reflows.
2. Web fonts with font-display: swap when swap font has different metrics from fallback (FOUT-induced shift). Web Almanac 2025: median site uses 4 fonts; only 0.5% use the CLS-safe font-display: optional.
3. Late-loading ads, embeds, cookie banners that inject above-the-fold content.
4. App-injected banners on Shopify and similar (promo bars, free-shipping bars).
5. Dynamically-loaded above-the-fold content from JavaScript (consent managers, geo-personalisation).

Remediation pattern: Reserve space with aspect-ratio or min-height → use font-display: optional with preload, or swap plus size-adjust metric overrides → place cookie banners outside document flow (bottom-anchored fixed) → audit every plugin/app that can inject above-the-fold DOM.