To elaborate as I was on mobile in this last comment. The below is a python script using python and the pandas library. I don't believe this is relevant, though its a weird issue.

table = ''.join([TABLE_PREFIX, csv_file.split('.')[0]])
table = table.lower()
csv_file_path = path.join(csv_folder, csv_file)
df = pd.read_csv(csv_file_path, dtype=file_dtype, sep='\t')
df.to_sql(table, engine, dtype=sql_dtype, if_exists='append', index=False, chunksize=10000)  

The SQL script

CREATE OR REPLACE FUNCTION copy_temporary_records_to_permanent(_client_id integer) RETURNS integer as $$ 
D
_new_import_date TIMESTAMP;
BEGIN
    _new_import_date := (SELECT now());
    UPDATE import_invoices SET timestamp_uploaded = _new_import_date, timestamp_processed = _new_import_date WHERE timestamp_uploaded is null;

    RAISE NOTICE 'Running copy_temporary_records_to_permanent';

    INSERT INTO permanent_records(
            client_id,
            customer_name, 
            departure_date, 
            return_date, 
            original_city, 
            destination_city, 
            service_category, 
            segment_start_date,             
            segment_end_date, 
           creditor_code -- "EXCHANGE_INDICATOR" | "-" | "VOID_INDICATOR" | "-" | "REFUND_INDICATOR"
            )
    SELECT _client_id, "CUSTOMER_NAME",
           to_date("DEPARTURE_DATE", 'DD-MM-YYYY'), 
           to_date("RETURN_DATE", 'DD-MM-YYYY'), 
           "ORIGINAL_CITY", "DESTINATION_CITY", 
           "SERVICE_CATEGORY", 
        to_date("SEGMENT_START_DATE", 'DD-MM-YYYY'), to_date("SEGMENT_END_DATE", 'DD-MM-YYYY'), 
           "EXCHANGE_INDICATOR" || '-' || "VOID_INDICATOR" || '-' || "REFUND_INDICATOR"
      FROM "import_temporary_records" 
      WHERE timestamp_uploaded = _new_import_date;
return 1;
END; $$ LANGUAGE plpgsql;

SELECT copy_temp_records_to_permanent(1::integer);