If you're a previous Blackberry user, then you were likely quite beholden to that company's secure messaging platform, BBM. That was such a popular messaging tool, in fact, that Blackberry produced clients for other mobile operating systems even as they struggled themselves to remain relevant in the market. Windows Phone even received a BBM messaging app, and until recently it remained available in the Windows Store.
That's changed, suddenly, as a tipster over at Windows Central noticed that the BBM app is no longer available in the Store. There's no reason given so far for the app's disappearance, which could either be a mistake or an intentional removal that could me a number of things--Blackberry could be removing support for Windows phone or preparing to release an updated UWP version.
That's all speculation at this point, however. If you're a BBM messaging user, however, let us know in the comments if you're seeing any changes with app and its support.