这个问题可能是因为响应中不包含Content-Length头部信息，导致无法知道下载进度而发生。解决方法是手动设置Content-Length头部信息。

示例代码：

axios.get(url, {
  onDownloadProgress: (progressEvent) => {
    let percentCompleted = Math.round((progressEvent.loaded * 100) / progressEvent.total);
    console.log(percentCompleted);
  },
  responseType: 'blob'
})
.then(response => {
  //手动设置Content-Length头部信息
  const contentLength = response.headers['content-length'];
  response.headers['content-length'] = contentLength ? contentLength : response.data.size;
  setTimeout(() => {
    console.log('This code will run after the download has been completed');
  }, 2000);
})
.catch(error => {
  console.log(error);
});