CXone /agents/states returns empty array for active agent

Stuck on a CXone integration where GET /api/v2/agents/states returns an empty array for an agent confirmed as logged in via the UI. Verified the agent_id matches the internal UUID and the auth token has valid scope for agent management. The payload is strictly [] with a 200 OK, ruling out authentication or endpoint errors. How do I debug why the API state diverges from the UI login state?