The internal pages you guys saw drop, were they ones that had been an SEO priority (i.e. you'd keyworded them and pointed links at them)?
the target page dropped for the PLURAL
version of the keyword (blue widgets) and was "replaced" in the SERPs by the home page at the same position. For the singular version of the keyword (blue widget), it still ranks in the same position.
Not necessarily an SEO priority. However, one of the keywords (blue) appears in the domain name as well as in the page name (w w w.exampleblue.com/blue-widgets.html).
There were no external links built to that page.
I did do some link begging to the home page, or to some article pages on my site which in turn link to the target page. Only got a handful of links in total (maybe around 10). But no EXTERNAL links directly to that page.
links DO have exact match PLURAL
anchor text to that page.
The keyword phrase [blue widgets] is repeated numerous times on the page, but it is a LONG page (like 12 paragraphs of text, each paragraph having between four and 6 sentences), and it would sound quite amateurish to use "it" and "them" repeatedly in lieu of "blue widgets"
Despite having fallen out of the SERPs for that keyword and losing its place as a LANDING page, it is still the second most popular page on the site, due to people following internal navigation / clicking internal links to the page, because it covers a subject that people who visit my site are interested in.