In current KeeneticOS version 5.0.11, every time a "Read only" user logs in, a notification shows up in the lower right corner saying "The current user doesn't have permission to change device settings.". This (unnecessary) notification is exactly in the position where it hides the logout button, so the notification has to be dismissed just to be able to log out.
Please either allow the notification to be dismissed permanently, or at least move it to a place where logging out is possible without dismissing it.