The Growing "Contentful" Gap
If you're measuring both First Contentful Paint and Largest Contentful Paint, this analysis of FCP versus LCP by Tim Kadlec is a must-read. The Google Chrome team recently made some changes to how they define "contentful" for Largest Contentful Paint. As a result, there's an even greater gap between the results you might see when you compare your First Contentful Paint results to your LCP results.
As Tim writes:
The reason why “contentful” has very different meaning in the context of LCP vs FCP is because while the two metrics sound very similar, they’re actually built on two different underlying specifications... Until and unless something happens to align the definition, it will be important for anyone measuring both FCP and LCP to remember that, in this case, contentful in one doesn’t equal contentful in the other, and that may lead to some odd disconnects.