Stock messaging bounces to blank new message

[AC Question]

LG V20 Nougat stock messaging is acting strange. Whenever the screen times out or I turn it off with a message thread displayed, it reappears with a blank new "compose" window waiting for a recipient to be entered. I have to hit "back" then find the thread in my list and reopen. Its becoming a real pain. I've downloaded and chosen Google messages as my default (but it wouldn't load all of my outgoing message history) then went back again but same problem. I'm nervous to lose all our some of my history. Any ideas? Thanks.