I'm sure some have seen the news over the weekend about the latest issue with the Boeing 737 Max series 

As a frequent flyer in Boeing 737's I've taken an interest in this story as to be honest it's confirmed by thinking behind why I ALWAYS have my seatbelt fastened throughout the whole flight (unless getting up to use the facilities that is) 

From the news reports I've read it seems that an emergency door blew out from the rear section of the plane. The Max 9's are similar to the Max 8's I believe in that there is an additional emergency exit between the over wings exits and the tail end of the plane and it's one of those doors that was the problem. 

Why would that be though? That's not a door that's use for entry into the aircraft unlike the front and rear doors so would have been fully secured surely? Could it be faulty design or materials failure? Or human error during construction maybe?