Lab Data
A synthetic test, loads the page and does a few tests, it is purely a diagnostic tool.
Origin Summary
Real world data collected from real browsers.
This data is for the whole domain not just this page
Also in the real world CLS data is collected from the second the page loads until the page unloads.
For this reason if you have layout shifts further down the page then they will show.
This data also includes multiple screen sizes so you may have a layout shift at a tablet screen size that the synthetic tests are not picking up.
Finally as "Origin Summary" is across the whole website not this one page, you could possibly have a page elsewhere that has a large CLS that is impacting your origin summary.
The final thing to note is that the Origin Summary shows you a mini bar graph where:
- 84% of page visits have a low CLS score (a pass)
- 4% of page visits have an average CLS score
- 12% of page visits have a poor CLS score
This points to either a poor performing page with a very high CLS or the site having issues at certain screen sizes.
You need to test for both of these.
You may want to consider using the web vitals library to collect real world data and link it with screen size data, scroll data etc. in order to identify the cause of your CLS issues.