Cognito: VerifyUserAttribute 'email' responds with InternalServerError when using another email already in the pool

Question

In our Cognito instance we define the 'email' as the username. We implemented a workflow, that the user should be able to change the email-address. When the user takes an email address already used in the pool and a valid Code. We get in InternalServerError.
(See: https://docs.aws.amazon.com/cognito-user-identity-pools/latest/APIReference/API_VerifyUserAttribute.html)
My Expectation would be, that that there is an AliasExistsException.
Can you verify, that this is a bug in Cognito?

Answer

This should be due to the AliasExistsException. Cognito's error handling is not complete or known to be very descriptive. While the error is not well described, this is not a bug per se, but rather poor description for error handling.

Cognito: VerifyUserAttribute 'email' responds with InternalServerError when using another email already in the pool

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