Vega-Lite Aggregate stopped working after upgrade to 7.10 (from 7.6)

[brunet (Ferran Brunet)]

Dears,
I had a nice bubble vizs with Vega Lite which stopped working after upgrading to 7.10.
The _docs are gathered ok from the index. But when transform/aggregate/sum is processed within Vega, undefined values appear everywhere.

Here the source_0 well populated:

Here the data_0 with undefined data:

If i run debug at console and open nodes section I see when the data get lost....

How the answer looks like:

It was working before the upgrade (vega lite v2 (kibana 7.6) ---> vega lite v4 (kibana 7.10)).
Any help would be very much appreciated.

Here the spec:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
   "data": {
    "url": {
      %context%: true
      %timefield%: @timestamp
      "index": anindex*
      "body": {
             _source: [ "cost",  "id1", "category1",]
       }
    }
   "format": { "property": "hits.hits" } 
  },
  "transform": [
    {
      "aggregate": [
      {
        "op": "sum",
        "field": "_source.cost",
        "as": "totalcost"
      },
      {
        "op": "distinct",
        "field": "_source.id1",
        "as": "id1qty"
      }
    ],
      "groupby": ["_source.category1"]
    },
    
    {
      "calculate": "datum.totalcost/datum.id1qty",
      "as": "cost_per_id1"
    }
]