When I query multiple instruments with get_data I get an error, whereas one instrument returns data. I have included the relevant queries below. This looks like a bug or at least some odd undocumented behaviour.

eikon.get_data(
  ['0#CS-PADD1-US',],
  ['CRD_STREAM'],
  raw_output=True
)

{
  "columnHeadersCount": 1,
  "data": [
    [
      "PD1ABOCRDSLT",
      "Abo"
    ],
    [
      "PD1AGBCRDSLT",
      "Agbami"
    ],
...
  ],
  "headerOrientation": "horizontal",
  "headers": [
    [
      {
        "displayName": "Instrument"
      },
      {
        "displayName": "CRD_STREAM",
        "field": "CRD_STREAM"
      }
    ]
  ],
  "rowHeadersCount": 1,
  "totalColumnsCount": 2,
  "totalRowsCount": 187
}

Whereas querying multiple series I get field errors.

eikon.get_data(
  ['0#CS-PADD1-US', '0#CS-PADD3-US'],
  ['CRD_STREAM'],
  raw_output=True
)

{
  "columnHeadersCount": 1,
  "data": [
    [
      "0#CS-PADD1-US",
      null
    ],
    [
      "0#CS-PADD3-US",
      null
    ]
  ],
  "error": [
    {
      "code": 251658244,
      "col": 1,
      "message": "Error: Field 'CRD_STREAM' was not found in response for the instrument '0#CS-PADD1-US'",
      "row": 0
    },
    {
      "code": 251658244,
      "col": 1,
      "message": "Error: Field 'CRD_STREAM' was not found in response for the instrument '0#CS-PADD3-US'",
      "row": 1
    }
  ],
  "headerOrientation": "horizontal",
  "headers": [
    [
      {
        "displayName": "Instrument"
      },
      {
        "displayName": "CRD_STREAM",
        "field": "CRD_STREAM"
      }
    ]
  ],
  "rowHeadersCount": 1,
  "totalColumnsCount": 2,
  "totalRowsCount": 3
}

The respective payloads of the queries are

{'Entity': {'E': 'DataGrid_StandardAsync', 'W': {'requests': [{'instruments': ['0#CS-PADD1-US'], 'fields': [{'name': 'CRD_STREAM'}]}]}}}
{'Entity': {'E': 'DataGrid_StandardAsync', 'W': {'requests': [{'instruments': ['0#CS-PADD1-US', '0#CS-PADD3-US'], 'fields': [{'name': 'CRD_STREAM'}]}]}}}