Having some issues with the previous update for BBM? If so, you'll want to get the newest version available that has now arrived in BlackBerry World. Noted as v10.11.6.21, this release uses the same changelog from the previous release, so while it's hard to say what exactly has changed, it's safe to say there are some bug fixes in there as there always is with any update.
Spot anything specific that has changed? I had some issues with groups not working correctly, and they appear fixed in this build, so there's that. Sing out in the comments and let others know if you had some bugs that are now fixed in this build. The update should be showing for everyone by now, if not, just go ahead and refresh BlackBerry World or search for BBM and it should appear for you.