I’m posting this here as suggested in response to my ticket that already reported the issue (case EU68331485).
Whenever I log in in the map editor, I’m logged out in the game, and vice versa. The game tells me I’m logged in from another computer, but this is not the case - I’m using both programs from the same machine (for map making and testing, naturally). I’m on macOS 10.15.1, SC2 version 4.10.4 build 76811, using the EU region, logging in with email+password.