In order for ORGs to be accessible via a drop-down menu (Organization Menu), it is necessary to make sure that the user passwords match in every ORG. It is possible to log into each ORG and manually change the user's password or reset the default admin user password from the console (using the netdiag login).
Once the passwords match, it is necessary to logout and back in to see the available ORGs via the organization drop-down menu (fast switch). Please also note that in order to use this feature, it is first necessary to enable the setting "Show organization menu in admin header" from the System Console | Settings | General Settings.
Note: Opening several tabs on the same browser, between SystemUI and Admin/User UI will cause both sessions to kick each other out due to session mismatch. This is by design to avoid unauthorized access by session hijacking. To use both at the same time, open them on separate browsers (For example, Chrome & Edge). Two separate windows on the same browser will still kick both sessions.