updateData always adds but never updates records

I defined resultid key in mapping to be an id key. This is not a unique key but I need it to identify groups of records:

var mapping = {
  resultid: {
    type: "id"
  }
};

But when I try updating it, it never does that, instead always adding to the end of the data array:

me.flexview.updateData({ data: [{...}] }, { partial: true })

The full code is provided below:

scil.Registration.ajax("flexview.getimagestructures", function (ret) {
  ret.data.forEach((imgData) => {
    var { resultid, compoundid, structureimage } = imgData;
    var currdata = me.flexview.getReport().dataSource.data;
    var entityidcolname = me.flexview.getReport().slice.rows[0].uniqueName;
    var dataForUpdate = currdata.find(d => {
    if (resultid > 0)
      return d.resultid == resultid
    else
      return d[entityidcolname] == compoundid;
  });
if (!scil.Utils.isNullOrEmpty(dataForUpdate)) {
  dataForUpdate["structureimage"] = structureimage;
  me.flexview.updateData({ data: [dataForUpdate] }, { partial: true });
}
else
  console.error(`Could not find item with resultid: ${resultid} and compoundid: ${compoundid}`);
});
me.flexview.refresh();
}, { compoundids: newCompoundIdsStr });

What I am trying to do is just updating "structureimage" key for all keys "resultid" when expanding a row.