Client script grabbing data from wrong child table entry

ERPNext
2

I think, your script isn’t working properly because it’s running too early, before all the data is fully loaded. Instead of using onload_post_render, try using the refresh event, which ensures everything is loaded.

Try it.

frappe.ui.form.on('jobnum', {
    refresh: function(frm) {
        if (frm.doc.phase && frm.doc.phase.length) {
            const options = frm.doc.phase.map(row => row.data_rcui);
            frm.fields_dict['second_child_table_name'].grid.update_docfield_property('po', 'options', options);
        }
    }
});