Json Deserialization failed on token and has left off in the middle of parsing a row

Question

I am trying to bulk load a csv file with 11000 records using Python with the simple-salesforce API.

The error that I am running into is that when I try to load the file, I get this message:

{'created': False,
  'errors': [{'fields': ['external_field__c'],
              'message': "Json Deserialization failed on token 'external_field__c' "
                         'and has left off in the middle of parsing a row. '
                         'Will go to end of row to begin parsing the next row',
              'statusCode': 'INVALID_FIELD'}]

I am able to load just one record using my code, but anything greater than 1 then I get the JSON Deserialization error. I have validated that the API name in the Object Manager is the same as what I am trying to upload.

This is my code:

from simple_salesforce import Salesforce
from pprint import pprint
import json
import pandas as pd
from pandas import json_normalize
from sfbulk2 import SFBulk2
import requests
import csv
from salesforce_bulk import CsvDictsAdapter


load_data = pd.read_csv('C:\\Users\\BlahBlah\\Desktop\\test_csv4.csv')   
load_data = load_data.fillna('')
print(load_data)
bulk_data = []
for row in load_data.itertuples():
    d = row._asdict()
    del d['Index']
    bulk_data.append(d)

sf = Salesforce(username='username', password='password', security_token='token', domain='test')    
x = sf.bulk.Account.upsert(bulk_data,batch_size=10000, external_id_field='external_field__c')
pprint(x)

I am thinking that there might be something very simple I could be missing with this code, but I have tried to research this issue for hours without getting anywhere.

Edit Adding "fake" data:

external_ID__c,LastName,FirstName,MiddleName,PersonBirthdate,RecordTypeId,Phone,PersonMailingStreet,PersonMailingCity,PersonMailingState,PersonMailingPostalCode,PeronMailingCountry
9999,SMITH,JOHN,,1970-01-01,XXXXXXXXXXXXXXX,99999999999,123 ANY STREET,ANYTOWN,NY,10001,USA```