That is a Google IP address. What user agent was used for the visit? That can tell you more about whether it was a human being. Als,o you could check the raw logs to see what files were requested - just the html file or html plus images, css, js etc.
I doubt that a gradual loss of pages would be connected to Adsense. That sounds more like the kind of scenario that has been frustrating for so many here for the past two months. Adsense problems would be handled by the Adsense teams. If you want to read about others with the vanishing pages syndrome, one of the first (and longest) threads begins here: [webmasterworld.com...]