We are using Graph API to allow an in-house workflow to reply to users who initiate a chat with a Facebook webpage. Along with some messages, we also send suggested responses to the user. When messages are initiated to the webpage via Android Messenger, the suggested responses only appear for the user a long time after the prompt or when the user re-opens the Messenger app or chat head.

This seems to be exclusive to Android messenger as the phenomenon is not observed if the user send the message through iOS Messenger app, a desktop browser or the desktop Messenger app.