I am getting the same since the Carnival update. It is irritating because you have to keep checking to see if there is a new message. Usually there is not. If I check the messages the exclamation point goes away, but as soon as I go to the map or another screen and come back, or close and open the game, the exclamation point is there again with no new messages.
I am on iPad (6th generation) with iOS version 13.3.1.