macOS - "Failed to connect to instance" error

This seemingly worked for me:

Log in to character selection, go to options and change Render Resolution to No Upscale before clicking play. The game may need to be full screen, I don't know. You can switch back in game.

Could have been completely random, but I do think there's something going on with the Render Resolution because it also changes from 56 to 59% when I don't get in and the blurry load screen fits a resolution issue.