http://www.newsweek.com/facebook-messenger-updating-crashing-open-ios-version-170-bug-979710

Facebook Messenger users: You may want to hold off updating to the latest version of the Messenger app. The new Messenger update—version 170.0—was released to iOS users on June 14, and they are reporting the app is extremely buggy and crashing often. 

Facebook said it was aware of the Messenger crash bug and was working to roll out another update that will fix the issues. Users who have not updated to the latest Facebook Messenger version, appear to not have any reported issued.