I received the following email from Amazon that I think points the root of this problem. Unfortunately, I don’t have a solution.
Thank you for being a valued Alexa partner. The purpose of this email is to inform you of an upcoming change that may impact live skills using the ‘ userId’ attribute, an pseudonymized identifier (present in the skill request JSON) that refers to an Amazon account for which your skill is enabled. If your skill does not have any business logic leveraging the ‘userId’ attribute, this change is not relevant to you, and you can ignore this message. If you are not sure, please review our technical documentation here or feel free to reach out to https://alexa.design/contactus with your skill ID for help.
What are we changing?
In our effort to continually improve end-user experiences, we will be migrating to a new cryptographic algorithm for userId on 10/25. As a result, the length of the userId string will change from 255 characters up to 356.