Sounds like a serial comms failure to me. 
Are you using an ESP32 module with a USB connection cable?
Try reducing the upload speed (vMicro Upload speed) to something lower and try that.

What module/version of ESP32 are you using?

Yes, using USB cable.
SparkFun Thing Plus - ESP32 WROOM
Upload speed:115200 I think this is the lowest setting in VM.
CP2104 driver: 11.1.0.53

Upload is failing every time today with:
esptool.py v3.1
Serial port COM8
___
A fatal error occurred: Failed to connect to ESP32: Timed out waiting for packet header

I thought I had solved this last week after I changed Remote Transport to Bridge in project properties and it worked but it failed again today.

Serial output continues to work fine for app previously uploaded to ESP32.

Thanks.

I changed the driver to Windows version 6.7.6 but am still getting same error. Any ideas?

I’m confused about which is the correct driver. Sparkfun say that it should be a version at or above 10.1.3.2130 and their link sends you to the Windows Universal Version.

https://learn.sparkfun.com/tutorials/esp32-thing-plus-hookup-guide?_ga=2.2332489...

Thanks 

Thanks. I have emailed you the output file when using driver v6.7.6.

Thanks. I've updated VM to the latest version but still have the same issue. I'll email the output file. Output is using 11.1.0.53 Universal Windows driver but can swap back again 6.7.6 again if you need the output from that.

It's very odd. Got it to upload once yesterday using previous version of VM and driver 11.1.0.53 but when I repeated the upload it failed. I'll attached the upload output for that too.

Many thanks

Sorry for the delay. Simon from vm will review first thing next week.

Can you confirm if this works normally in the Arduino IDE, or whether this suffers the same issue?

Thanks for confirming. This means it is not an issue with Visual Micro directly, and we have been unable to replicate this on similar ESP32 boards on our side to investigate further.

From what we can see the settings look right, the upload process is handed over to the esptool.exe, so the upload can also be run from the command line to remove Visual Micro / Arduino IDE from the equation completely (this is seen in the output after enabling vMicro > Uploader > Verbose, and performing an upload in vMicro).

We do not have the specific Sparkfun board, however our ESP32 Dev Module has an ESP32 chip, and the same CP210x port.

Currently we are running the 11.1.0.53 driver, but found no issues with 10.1.10.103, or 6.7.6.2130 either.

As it has worked correctly for you a couple of times, have you tried the below options to troubleshoot?
a) Changing the USB lead
b) Changing the port it is connected to on your PC (ideally not through an external USB hub)
c) Remove all external connections from the board
d) Upload a very simple sketch (e.g blink)

Thanks for the update and solution clarification on this aspect.

It is very confusing their guide says the auto reset should work, when this solution shows it clearly doesn't. They are working on improving the new esp32 board cores, it might be one to report on their github site.