Some of the messages I have sent to Facebook friends are appearing with 'seen' stamp if I open the messages on facebook.com while they are unseen on the Messenger app. Which one is the right one? It seems to me that messenger is right because on Facebook, all the times when the message is seen is one minute after sending the message. 
'seen' message status on Facebook website and Messenger app
facebook;facebook chat
Reinstalled Messenger and logged in again and it should work.