On August 27. 2017, Nogizaka46’s official website unintentionally posted an internal staff LINE chat on this page (they took it down quickly, as one would expect): http://www.nogizaka46.com/news/releases/
We translated the contents of the LINE chat (presented side-by-side with the original Japanese screenshot). Members are mentioned, but there’s no serious scandalous material (except that Akimoto Manatsu has an “erotic” persona behind the scenes, Sasaki Kotoko is technologically challenged, and Nishino Nanase could be a diva). It gives a brief look into what’s keeping staff busy these days and how they refer to and discuss the member idols. The biggest aftermath among Japanese fans is ire at how silly and unprofessional the staff were to have allowed such a leak to happen. The best guess as to how it happened is that a staff member meant to copy text (a blurb about the Asahinagu movie) and paste it into the official website but instead of copy they hit screenshot and pasted that in. Voila.
Here is a link (archived) to a Japanese webpage that covered it as it occurred (taking excerpts from 2channel). Someone posted a screenshot from their mobile of the page when the LINE chat was still posted on the official website.