我的之前也是报这个错 然后重新搞了下又可以了

let link = 'https://dfs.dev.8atour.com/group1/M00/01/95/wKgeyV7i9HaAZounADY0rmP6X1c988.mp4';
    wx.downloadFile({
      url: link,
      success: res => {
        console.log('downloadFile成功',res);
        wx.showLoading({
          title: '获取资源中',
        })
        const $pop_details = this.getElementsById('pop_details')
        $pop_details.reset()
        
        wx.saveVideoToPhotosAlbum({
          filePath: res.tempFilePath,
          success: file => {
            console.log('saveVideoToPhotosAlbum成功',file);
            wx.hideLoading()
            wx.showToast({
              title: '下载成功',
              icon: 'none',
            })
          },
          fail: err => {
            console.log('saveVideoToPhotosAlbum失败',err)
            if (err.errMsg === 'saveVideoToPhotosAlbum:fail auth deny') {
              wx.showModal({
                title: '提示',
                content: '需要您授权保存相册',
                showCancel: false,
                success: data => {
                  wx.openSetting({
                    success(settingdata) {
                      if (settingdata.authSetting['scope.writePhotosAlbum']) {
                        wx.showModal({
                          title: '提示',
                          content: '获取权限成功,再次点击下载即可保存',
                          showCancel: false,
                        })
                      } else {
                        wx.showModal({
                          title: '提示',
                          content: '获取权限失败，将无法保存到相册哦~',
                          showCancel: false,
                        })
                      }
                    },
                  })
                }
              })
            }
          }
        })
      },
      fail:res=>{
        console.log('downloadFile失败', res);


      }
    })

我也是，android iOS 都存在这个问题