Vega-Lite bar chart doesn't show anything for filters aggregation

Hello,

In my Vega-Lit spec I do a query which returns the following response:

  "aggregations" : {
    "my-groups" : {
      "buckets" : {
        "group-1" : {
          "doc_count" : 16958
        },
        "group-2" : {
          "doc_count" : 3248
        },
        "group-3" : {
          "doc_count" : 408
        }
      }
    }
  }
}

I have a Vega-lite barchart like that:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": 
  {
    "url": {
      # Query which returns the above result 
    },
    "format": {
      "property": "aggregations.my-groups.buckets"
    }
  },
  "transform": [{
    "fold": [
      "group-1",
      "group-2",
      "group-3"
    ]
  }],
  
  "mark": bar
  "encoding": {
    "x": {
      "field": "key",
      "type": "ordinal",
    },
    "y": {
      "field": "value.doc_count",
      "type": "quantitative"
    }
  }
}

The confusing thing is, that I see a result on 'Vega-Lite-Editor' but not in Kibana itself.
It shows just a X-Axis, a Y-Axis, and nothing more.
The following example can also be displayed in the Online Editor, but not on Kibana.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": {
    "values": [{
      "buckets" : {
        "CERTIFICATE" : {
          "doc_count" : 167523
        },
        "MSCERTIFICATE" : {
          "doc_count" : 4865
        }
      }
    }]
  },
  "transform": [{
    "fold": ["buckets.CERTIFICATE", "buckets.MSCERTIFICATE"]
  }],
  "mark": "bar",
  "encoding": {
    "x": {
      "field": "key",
      "type": "ordinal"
    },
    "y": {
      "field": "value.doc_count",
      "type": "quantitative"
    }
  }
}

This works for me in Kibana. What version are you using?