Note by Frank Nimphius, October 2018
For everyone building chatbots using Facebook Messenger as a client. The following alert will be added to our product documentation but may impact you already.
"Changes to the Facebook User Profile API require that you now must request permissions for certain user profile fields for any Facebook app that you created before or after July 26, 2018. Without the following permissions, the user's name will be populated as a random numeric string.
pages_messaging
pages_user_locale
pages_user_timezone
If you created the app before July 26, you have until January 29, 2019 to apply the permissions. If you created your app after July 26, 2018, then you need to add these permissions as soon as possible. You can set them in the App Review for Messenger section of the Messenger page."
So if you run Facebook as a messenger and the profile.firstName and profile.lastName variables don't return the user first name and lastname, but an ID string, then the reason is a change of the Facebook permissions.
