If you see an orange line on your History Center chart with the label "Puppeteer Browser Service changed", it means that Acquia Optimize has started scanning your domain with a new generation browser service technology called "Puppeteer".
A browser service is an automatic tool that Acquia Optimize uses to render and crawl your website. It provides the basis for finding issues on your website and reporting them to you through the Acquia Optimize UI.
With the new generation browser service, Acquia Optimize is able to provide more accurate crawl results, even for websites that have a very complex structure. This also means that we may find more issues on your domain than when we were scanning with the previous browser service. In other words, you may see a slight jump in issue count as a result of moving to the new browser service.
Read this article for more information about the Puppeteer service and how it works
For more information, see the user guide article:
History center