Is your Web Dev Tools showing a better score than page speed insights?
Continuing what @henryp25 said above. “Lab tests” is often when you run against a local server or machine and so the latency will drop considerably. Page Speed Insights could be anywhere google has servers and may not be close to your origin, and therefor increased latency will delay the LCP, potentially delay TTI (especially if you have external styles and scripts) and can therefor push out your CLS if slower loading assets causes more layout shifts (again especially with external stylesheets, preventable with critical styles in line on page).
Even if both tests are being run on the same “production” instance, still you might be geographically closer to your origin server than the page speed insights servers.
As an example, I live in the same city as the authors of GTMetrix. My Vancouver GTMetrix scores are better than any other testing tool online - mostly because TTFB on all requests is < 50ms due to geographic proximity.
If I run WebPageTest on my site using a more eastern US location, TTFB from origin can jump up to 500-600ms which is when having a CDN (CloudFlare) and proper caching headers help.
One more tip I heard from John Mueller on SEO Office Hours mention: The chrome dev tools capture the entire user experience including user interactions. So CLS will change if you have things like auto-refreshing adds or adds injected into content as you scroll, etc. Whereas automated testing tools generally have a fixed viewport that doesn’t change and will never interact with the page (such as a scroll event) which may cause some scripts to not fire resulting in slightly better stats in these cases.
I suppose that brings up one more thing too, your local viewport and the testing tool’s viewport may not be the same which could shift what is being measured for LCP or change how many images are loaded via various deferred loading techniques, etc.
I’d be curious to hear a more specific complaint from you like which tool was giving the better scores for you.