Custom button, service dialog drop down values are missing

gistfile1.txt

{
  "href": "https://10.8.198.232/api/service_dialogs/2",
  "id": "2",
  "description": "desc",
  "buttons": "submit,cancel",
  "created_at": "2018-05-03T20:27:27Z",
  "updated_at": "2018-05-03T20:27:27Z",
  "label": "multi",
  "content": [
    {
      "href": "https://10.8.198.232/api/service_dialogs/2",
      "id": "2",
      "description": "desc",
      "buttons": "submit,cancel",
      "created_at": "2018-05-03T20:27:27Z",
      "updated_at": "2018-05-03T20:27:27Z",
      "label": "multi",
      "dialog_tabs": [
        {
          "href": "https://10.8.198.232/api/service_dialogs/3",
          "id": "3",
          "created_at": "2018-05-03T20:27:27Z",
          "updated_at": "2018-05-03T20:27:27Z",
          "label": "New tab",
          "dialog_id": "2",
          "position": 0,
          "dialog_groups": [
            {
              "href": "https://10.8.198.232/api/service_dialogs/3",
              "id": "3",
              "created_at": "2018-05-03T20:27:27Z",
              "updated_at": "2018-05-03T20:27:27Z",
              "label": "New section",
              "dialog_tab_id": "3",
              "position": 0,
              "dialog_fields": [
                {
                  "href": "https://10.8.198.232/api/service_dialogs/19",
                  "id": "19",
                  "name": "dropdown_list_1",
                  "description": "",
                  "data_type": "string",
                  "display": "edit",
                  "display_method_options": {},
                  "required": false,
                  "required_method_options": {},
                  "default_value": "",
                  "values_method_options": {},
                  "options": {
                    "sort_by": "value",
                    "sort_order": "ascending",
                    "force_multi_value": false
                  },
                  "created_at": "2018-05-03T20:27:27Z",
                  "updated_at": "2018-05-03T20:27:27Z",
                  "label": "Dropdown",
                  "dialog_group_id": "3",
                  "position": 0,
                  "reconfigurable": false,
                  "dynamic": true,
                  "show_refresh_button": false,
                  "load_values_on_init": false,
                  "read_only": false,
                  "auto_refresh": false,
                  "trigger_auto_refresh": false,
                  "visible": true,
                  "type": "DialogFieldDropDownList",
                  "resource_action": {
                    "resource_type": "DialogField",
                    "ae_namespace": "System",
                    "ae_class": "Request",
                    "ae_instance": "InspectMe",
                    "ae_attributes": {}
                  },
                  "dialog_field_responders": []
                }
              ]
            }
          ]
        }
      ]
    }
  ],
  "actions": [
    {
      "name": "refresh_dialog_fields",
      "method": "post",
      "href": "https://10.8.198.232/api/service_dialogs/2"
    },
    {
      "name": "delete",
      "method": "post",
      "href": "https://10.8.198.232/api/service_dialogs/2"
    },
    {
      "name": "edit",
      "method": "post",
      "href": "https://10.8.198.232/api/service_dialogs/2"
    },
    {
      "name": "copy",
      "method": "post",
      "href": "https://10.8.198.232/api/service_dialogs/2"
    },
    {
      "name": "delete",
      "method": "delete",
      "href": "https://10.8.198.232/api/service_dialogs/2"
    }
  ]
}