I'm currently running into an issue that prevents me from logging in at all, when running nerd login it opens an empty browser window. When running the underlying os command from the shell (e.g: open http://localhost:9876/oauth?state=P7gbZDSToiLiCKURgAhcPVAsXy7WAnPp) the same thing happens. This makes me believe this is outside of our control.
Also, it is not clear which browser session it will open. Maybe you have multiple sessions in different tabs (cognito)