Google has recently updated the cumulative layout shift scoring intending to improve on its accuracy. A Cumulative Layout Score (CLS) is a measurement of how often the web page elements jump around on a web page. Read more at www.searchenginejournal.com
One of the possible causes for this shifting could be the improper height and width of the images declared in the HTML. These images on downloading might expand, causing the web page elements to move, and a user can't interact with a web page that is moving around.
With the help of the CLS metric, you can now measure how much a page moves. Google has recently reviewed three solutions for updating the scoring process for CLS.
Google follows a Session Windows approach when it comes to measuring CLS. These session windows correspond to different parts of a web page that the user reaches while scrolling down the web page. The recent update by Google will only make the new scoring system more fair and accurate.