Everything was alright until level 604. Then out of nowhere chat box (looks like a mobile chat version) appeared at the bottom of the screen. I can’t close/disable it and it doesn’t function. Main chat area/window keeps working properly.
What the heck is that? Or more importantly how to fix that?
Menu > Settings > General > Leave Game
That will put you back to the Hero selection screen.
Re-enter the game, and the middle-centre chat box will be gone.
This is a long-standing bug on the PC client.