I see no onUserAuthenticateFailure trigger anywhere in Joomla. It's onUserAuthorisationFailure (permission check failed) and onUserLoginFailure (login it self failed) which CB does fire. We use Joomla API for the login so it's not possible for CB to not fire the Joomla login triggers.

There is no onUserAuthenticateFailure event in Joomla.

docs.joomla.org/Plugin/Events/User

If they're trying to act on onUserAuthenticateFailure it won't work with anything as that event does not exist. My previous reply contains the events they should be using; one is fired (onUserAuthorisationFailure) if the user doesn't have the Site Login permission and the other (onUserLoginFailure) is fired when login fails and both will fire from CB (as again we're using Joomlas own API to login a user).

CB doesn't attempt to login if there's no one to login. We don't bother asking Joomla if the credentials are valid when we know the user doesn't exist. There are no plans to change this behavior. In this case CB fires its own trigger onLoginFailed. So your extension would need to integrate with CB or attempt to do whatever behavior you're needing using CB Auto Actions and a Code action acting on onLoginFailed, which will let you use PHP to execute any necessary APIs.