I've had this happen often...it seems the text/email is triggered when they are ready to start boarding, or think they are, then all of a sudden they aren't due to catering not being completed or whatever other issue...very frustrating if the gate is a hike from the MLL. Made even more so if they are say trying to board a 777 HD at D24 at YYZ and you have 400 people crammed into a space that was designed to board a 319.