Actually the key is the Facebook Messenger itself. Because besides the iOS 11 users, people using iOS 10.3 devices also meet such problem. So if after the latest iOS 11.1 upgrade, your Messenger still keeps crashing. Try the tips in the post to fix the Facebook Messenger crashing issue. How to Recover Lost Data after iOS 11 Update
https://www.primosync.com/daily-tip/fix-facebook-messenger-crashing-on-ios-10.htm

