DataDownloader下载的分钟数据和回测时订阅的分钟数据不一样？

rb2005, 用DataDownloader下载的数据是有21:00:00的，但是回测的时候打印每个分钟k的datetime如下：

可以看到，是没有21:00:00这条k的(也就是日盘收盘)。我个人倾向于回测时少了一条数据。

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from datetime import date, datetime, timedelta
from contextlib import closing
from tqsdk import TqApi, TqSim, TqAccount, TqBacktest, TargetPosTask
import numpy as np
import pandas as pd
import math
import tqsdk
import time
 SYMBOL_A = "SHFE.rb2005"
 api = TqApi(TqSim(10000), backtest=TqBacktest(
    start_dt=datetime(2019, 12, 1, 8, 0, 0), end_dt=datetime(2020, 1, 11, 16, 0, 0)))
klines_a = api.get_kline_serial(SYMBOL_A, 60)
ticks_a = api.get_tick_serial(SYMBOL_A)
target_pos_a = TargetPosTask(api, SYMBOL_A)
  # 使用with closing机制确保回测完成后释放对应的资源
with closing(api):
     while True:
        api.wait_update()
        if api.is_changing(ticks_a):
            if api.is_changing(klines_a.iloc[-1], "datetime"):
                second_delta = klines_a['datetime'].iloc[-1]/1e9
                time_now = datetime.fromtimestamp(second_delta)
                print(time_now)