Arcade data expression in dashboard with Groupby function returns null values

[Arpa_PiemonteGeoportal_Team]

Dear All, I am trying  to calculate the sum of values grouped by two fields, however it returns null values and, in addition to this, it seems it doesn't group at all (see image attached).

Any idea?

My dahboard is running on Portal for Arcgis 11.1.

Thank you in advance.

Here is the code:

var myPortal = Portal('https://www.myportal.it/portal');
var itemId = '123456789';
var layerId = 0;
var fs = FeatureSetByPortalItem(myPortal,itemId, layerId,
['cod_reg','anno','csuolo8','clammi3_num'],false);

Console('Somma clammi3_num: ', sum(fs,'clammi3_num'));
Console('primo record: ',First(fs));

return GroupBy(fs, ['anno','cod_reg'], [
{name: 'sum_clammi', expression: 'clammi3_num', statistic: 'SUM' },
{name: 'sum_csuolo', expression: 'csuolo8', statistic: 'SUM' }
]);