@clemens just reminded me that I promised to drop some words about issues coming from insufficient or unstable power supply to ESP32-based modules and how to mitigate them. We researched this issue together with @tonke the other day, thanks!
Hint: If you are encountering problems like described here and you will not be able to make it work just by swapping the USB cable, a little amount of soldering might be involved.
To get started, the official documentation from Espressif has an appropriate troubleshooting section in its esptool documentation. Please read this carefully, especially when it comes to debugging issues revolving “stable power supply” after experiencing connectivity or responsiveness problems with your board.
Things might go south if power circuit fails to meet the large spikes of ESP32 power demand when using WiFi and/or when attached peripherals draw too much power.
Check your USB cable.
Check your power supply.
Apply the cap trick by adding a missing capacitor to your board.
For me it was a power issue, I am using a EzSBC esp32 dev board. Interesting it happens when I upload a sketch that requires a lot of pin usage. The way I “fixed” the situation was to apply 3v 2amp external supply to the 3v pin on esp32, plus an external ftdi to rx/tx, with common ground. Applying 5v 2amps to Vin on module did not solve the problem.
Fixing this issue already goes by “applying the cap trick” ;]. Enjoy.
Some third party ESP32 development boards use an automatic reset circuit for EN & GPIO pins, but don’t add a capacitor on the EN pin. This results in unreliable automatic reset, especially on Windows. Adding a 100nF (or higher) value capacitor between EN pin and GND may make automatic reset more reliable…