Same issue here on my side.
I'm running Visual Micro under Visual Studio Pro 2015. The OS is Microsoft Windows 10 64-Bit, Visual Micro states "version 1.1706.25".

I wanted to give ESP32 a try, but the modules were not recognized. So I updated the USB driver (dated 2017-11-15, version 10.1.1.1951) and finally the ESP32 have been recognized and I was able to program them (but I have to mention that I've used the Arduino IDE for that purpose so I'm not sure about ESP32 and Visual Micro Serial Monitor compatibility).

Next I wanted to switch back to my ESP8266 devices and encountered the exact issue mentioned by the original poster. Visual Micro compilation works (using the "Core Development Module"), download too, serial monitor not. Putty instead worked without any flaws.
After removing the suspicious USB driver and installing the older one (dated 2017-09-27, version 6.7.5.1893) the serial monitor is up and running as before.

From my point of view it is a Visual Micro issue. Strange is that even after closing and re-opening the serial monitor it is not able to connect to the serial port. But the port is not blocked by any party as Putty succeeds in any attempt.

Maybe the drivers timing has changed, and Visual Micro relies on the old behavior? Or some magic IDs which have changed?

Best regards,
Tobias

Thanks for the report

I have tested the SiliconLabs CP210x usb driver version 10.1.1.1951 on windows 10 and it fails to work with standard Microsoft C#

The driver throws an error suggesting it can only work with a baud rate of 9075

If you create a new windows forms c# project containing button1 and textBox1 then paste in the code below. Change the port from COM8 to your port you will see the problem.

Notice the baudRate iis set to 9075. Anything faster throws an error.

This is a driver issue however the fact that java from the arduino ide reads the port okay is annoying. I will investigate an alternative port reader but what we use is recommended by microsoft and well tried and tested (until recently)

Having said that. The 10.1 version is listed for windows universal and v6.7 listed for all other windows versions such as win10, win8, win7 etc.

https://www.silabs.com/products/development-tools/software/usb-to-uart-bridge-vc...

using System;
using System.Windows.Forms;

namespace WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        System.IO.Ports.SerialPort sp;

        private void button1_Click(object sender, EventArgs e)
        {
            sp = new System.IO.Ports.SerialPort("COM8");
            sp.BaudRate = 9075;
            // sp.BaudRate = 115200;
            sp.DtrEnable = false;
            sp.RtsEnable = false;
            sp.DataBits = 8;
            sp.StopBits = System.IO.Ports.StopBits.One;
            sp.Handshake = System.IO.Ports.Handshake.None;
            sp.Parity = System.IO.Ports.Parity.None;
            sp.ReadTimeout = 10;
            try
            {
                sp.Open();
                //sp.BaudRate = 115200;
                while (true)
                {
                    while (sp.BytesToRead > 0)
                    {
                        textBox1.AppendText(sp.ReadExisting());
                        Application.DoEvents();

                    }


                   System.Threading.Thread.Sleep(200);
                }
            }
            catch (Exception ex) {
                textBox1.AppendText(ex.ToString());
                System.Threading.Thread.Sleep(5000);
            }
            Application.Exit();
        }
    }
}