This is related to the “Viewed page” (PageViewed) activity. A PageViewedExtended event is logged when the same person continually views a web page for an extended period (up to 3 hours). The purpose of logging PageViewedExtended events is to reduce the number of PageViewed events that are logged when a page is continually viewed. This helps reduce the noise of multiple PageViewed records for what is essentially the same user activity, and lets you focus on the initial (and more important) PageViewed event.