Data Action JSON path mapping returning undefined

Architect & Flows
1 
{"path": "$.data.userId"}

Set this in a REST Data Action success output. The response body clearly has the field:

{"data": {"userId": "abc123"}}

Yet the Architect flow shows undefined when I try to map it to a variable. Tried $.data["userId"] too. Same result. The status code is 200. Is the SDK stripping nested objects before the JSON path evaluation happens?