This bug is present when you create a multiplayer game(custom game or maybe all types) alone or with computer players. It also happens when other players leave the game leaving you alone.
When I try to send message it doesn’t show in chat although it looks like it was sent.
Its painful for custom games where you rely on typing in chat for saving/loading game or other map specific commands.
I hope it is understandable enough to help you reproduce and fix this bug.