The app seems to start at a default size and position at launch, not the last one I used. Also its functions which launch in a web browser (blizzcon and the link to this feedback forum, for example) are requiring me to validate via authenticator when the app itself should do that.
The changing of size and position is very annoying. I hope it gets fixed soon.
I am using the High DPI version on a 4K monitor and as of today this is still not fixed. The main window and the chat windows revert to default every time they are opened.