SIL Custom field - how to use it in Dashboards (issue statistics)

[Abakus2020]

SIL custom field:

string[] result = system("/opt/getClient.sh " + clientId + " " + "&type=client_name");
return arrayGetElement(result, 1);

Searcher Template: Exact Text Searcher

All permissions have been checked. When running queries and  list views (also in Dashboard), all works fine. Also export to Excel works perfect. 

What does not work in Dashboards: Issue statistics returns the following error: 

The filter configured for this gadget could not be retrieved. Please verify it is still valid on the issue navigator.

Any idea what I am doing wrong?