Web Core Vitals and Page Speed Insights Not Matching Scores

[RMATVMC]

We have some URLs that are being flagged as poor inside Search Console in the Web Core Vitals report. For example, the report is saying that some pages have too many CLS issues.

When looking into things we can do to update we have noticed that when we run the same page using the PageSpeed Insights tool we are not getting the same bad scores. This is making it hard for us to actually know what needs to be addressed. Nor can we tell if a change actually fixed the issue because in PageSpeed Insights there is not an issue.  Has anyone else had similar issues. If so have you found a way to fix it?

[seoelevated]

To my understanding, GSC is reporting based on "field data" (meaning the aggregate score of visitors to a specific page over a 28 day period). When you run Page Speed Insights, you can see both Field Data and "lab data". The lab data is your specific run. There are quite a few reasons why field data and lab data may not match. One reason is that changes have been made to the page, which are reflected in the lab data, but will not be reflected in the field data until the next month's set is available. Another reason is that the lab device doesn't run at the exact same specs as the real users in the field data.

The way I look at it is that I use the lab data (and I screen print my results over time, or use other Lighthouse-based tools like GTMetrix, with an account) to assess incremental changes. But the goal is to eventually get the field data (representative of the actual visitors) improved, especially since that's what appears to be what will be used in the ranking signals, as best I can tell.