Worker isn't part of the queue specified in the Workflow target for re-targeted Task.
The Worker targeted by the Known Worker Routing feature is not a member of the TaskQueue referenced in the Workflow Target
Ensure the Worker is a member of the TaskQueue referenced in the Workflow Target. Find out more about the Known Worker Routing feature here: https://www.twilio.com/docs/taskrouter/workflow-configuration/known-agent-routing