When an AdSense gadget fails to appear in the Blogger layout after being added, it might be due to an ad blocker extension being active. Most browsers come equipped with ad blocker plugins or extensions designed to disable or block certain source codes or resources from Google or other ad-related remote sources. In my experience, I was setting up an AdSense gadget on my blog, but it didn't appear, even immediately after adding it. However, I later noticed that several AdSense ads were actually present when I visited my blog; they just weren't visible on the Blogger layout configuration page. Turning off my ad blocker extension in Chrome revealed that the ads were indeed there. Keep this in mind if you're unable to see AdSense gadgets in your Blogger layout.