原因找到了，应该是每一次查询时重新声明一次

createSelectorQuery，改成下面的就可以了

position(selector) {
  let that = this;
  let id = selector.substring(1)
  let query = wx.createSelectorQuery().in(that.parent.$root.$mp.page);
  return new Promise(function (resolve, reject) {
    query.select(selector).boundingClientRect().exec(res => {
      res.forEach((item)=>{
        if (item.id){
          if (item.id == id) {
             resolve(item);
          }
        }
      })

    });
  })
}