Payload validation error: List of roles IDs to associated with the user is too short in JS WebAuth.parseHash

I’m using auth0-js at version 9.16.2 in an Angular SPA. I recently deleted some unused roles in my Auth0 configuration so that now I have far fewer roles defined and most users have no roles. Since that change, I’m seeing this error intermittently in our logs:

Payload validation error: 'Array is too short (0), minimum 1' on property roles (List of roles IDs to associated with the user)."

I’ve traced the error to a call to parseHash on an instance of WebAuth but I’ve been unable to reproduce the issue in my dev environment. Having looked at the source of auth0-js I’m pretty sure this error is thrown server-side by the Auth0 API. Grateful for any advice that would help me track down the cause - I’m not sure at the moment whether this is causing loss of service to our customers.