使用数据下载工具下载多个合约时，CSV文件出现数据缺失，请问如何解决呢？

使用tqsdk.tools.downloader – 数据下载工具下载多个合约（超过10个）的历史数据输出到同一个CSV后，打开发现只有一两个品种有数据，其他显示#N/A，请问是什么原因呢？

如果是每个合约下载到单独的CSV，数据就没有问题。代码和CSV截图如下：

<span class="n">api</span> <span class="o">=</span> <span class="n">TqApi</span><span class="p">(</span><span class="n">TqSim</span><span class="p">())</span>
<span class="n">download_tasks</span> <span class="o">=</span> <span class="p">{}
</span>a1=["KQ.m@SHFE.au","KQ.m@SHFE.ag","KQ.m@SHFE.cu","KQ.m@SHFE.al","KQ.m@SHFE.zn","KQ.m@SHFE.sn","KQ.m@SHFE.ni","KQ.m@SHFE.ss","KQ.m@SHFE.rb","KQ.m@SHFE.hc","KQ.m@DCE.i","KQ.m@DCE.j","KQ.m@DCE.jm"]
<span class="n">download_tasks</span><span class="p">[</span><span class="s2">"daily"</span><span class="p">]</span> <span class="o">=</span> <span class="n">DataDownloader</span><span class="p">(</span><span class="n">api</span><span class="p">,</span> <span class="n">symbol_list</span><span class="o">=a1</span><span class="p">,</span> <span class="n">dur_sec</span><span class="o">=86400</span><span class="p">,</span>
                    <span class="n">start_dt</span><span class="o">=</span><span class="n">date</span><span class="p">(</span><span class="mi">2020</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="n">end_dt</span><span class="o">=</span><span class="n">date</span><span class="p">(</span><span class="mi">2020</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">12</span><span class="p">),</span> <span class="n">csv_file_name</span><span class="o">=</span><span class="s2">"daily.csv"</span><span class="p">)

</span><img src="https://www.shinnytech.com/wp-content/uploads/anspress-temp/00f7e6df6467ad13a60b107de1f9689c595c74d7_3709.jpg" />

感谢！