以下代码红色部分时不是的调用几次后就无法获取到openid了？

云函数部分代码如下：

const cloud = require('wx-server-sdk'

cloud.init({

  env: cloud.DYNAMIC_CURRENT_ENV

})

const db = cloud.database()

// 云函数入口函数

exports.main = async (event, context) => {

  const wxContext = cloud.getWXContext()

  let _openid = wxContext.OPENID;

  let action = event.action

  let taskClassNumber, record_date;

  if (action === 'get_status') {

    return getTaskStatus(_openid);

  } else if (action == 'get_task_Answer') {

    taskClassNumber = event.taskClassNumber

     record_date = await getToday()

//这里获取openid失败了

    console.log("wxContext.OPENID:",wxContext.OPENID)

    return getTaskAnswer(wxContext.OPENID, taskClassNumber, record_date)

  } else if (action == 'add_answer_record') {

    let recordObj = event.recordObj

    return addTaskAnswerRecord(_openid, recordObj)

  }