Unfortunately, Sandbox Personas does not support every attribute.
The Sandbox Personas dropdown will show all the attributes for enabled data services in the account. However, it does not currently filter for the attributes supported by Personas directly.
If the raw response does not show any coerced data from the persona, this may be due to using an unsupported attribute.
Please reach out to firstname.lastname@example.org if you need assistance in reviewing your Sandbox Persona.