I tried to reproduce and it worked as expected for me. Check your pipeline JSON to make sure your "clusters" spec there is explicitly mentioning the pool details.

Example:

  "pipeline_type": "WORKSPACE",
  "name": "mojama-dlt-classic-demo",
  "clusters": [
    {
      "label": "default",
      "instance_pool_id": "0602-190328-throe6-pool-guogi5jw",
      "policy_id": "000AA2BE733A7B2E",
      "driver_instance_pool_id": "0602-190328-throe6-pool-guogi5jw",
      "autoscale": {
        "min_workers": 1,
        "max_workers": 2,
        "mode": "ENHANCED"
      }
    }