Over the past few months Google has started to highly value one page on a site I maintain while the entry page continues to drop off steeply for pretty much every single other page. I've made no major changes and I haven't been able to find any suspicious third party activity thus far. I'm concerned this could effect the site in the long term because that page has little relevance compared to the rest of the site though it still serves a purpose for helping people. It could be any number of reasons, intentional or not such as putting too much emphasis on a page by a third party and then pulling-the-plug so-to-speak. I'm not really sure as I've never encountered this before. Suggestions on what I should look in to? The content on this site is all original and there is absolutely no advertising or any funny-business of any kind.
I've seen the same although it started in Dec 2012, and possibly sooner than that. Google has decided my site is about one subject and doesn't treat content about other subjects very well. Google's choice is actually a sub-topic of the main subject matter.
My backlinks remain the same, the site is over 10 years old.
The site was also deemed informational at some point, pages with product(either direct sales or affiliate links) are virtually ignored, regardless of age and despite some excellent all natural link profiles. I suspect my ability to rank about things not directly related to Google's choice, on this site, has been reduced. Or perhaps that's the norm and I've actually earned the right to be an authority on the one sub-topic? Only Google knows.