Cumulative Layout Shift CLS not improving / updating in Core Web Vitals Assessment after 28 days

Question

I have a very basic page which contains only text. The page content has not changed for past few months now and the CLS score in the section "Core Web Vitals Assessment" is:

For Mobile: 0.29
For Web: 0.16

But the CLS score in the metrics under the section "Diagnose performance issues" is:

For Mobile: 0.001
For Web: 0.036

And Core Web Vitals show past 28 days data collection. "Computed from the Core Web Vitals metrics over the latest 28-day collection period."

Despite having a Good CLS score in Metrics "Performance", the Core Web Vitals show Poor score.

What can I do to reflect the change?

Answer 1

The top score is based on real user experiences aggregated over 28 days.

The lower score is based on a single lab test emulating a typical user that does not interact with the page. This means it often does not trigger CLS issues that real users do.

Tools like the Web Vitals chrome extension can help you spot layout shifts as you interact with the page. Or you can add your own Web Vitals tracking code and see what elements cause layout shifts for your real users.

https://web.dev/vitals-ga4/