there are 3 devices, 2 of them are no longer working as no way to enter boot loading mode, re-flash firmware is rendered impossible.
attempted to uses ESP-IDF, and manually pull down GPIO0 and press RESET to enter boot loading mode, still does not work.
it is a bit disappointed for such devices and the reliability, about 2 years’ service life or less. either CP2104 failure or the ESP32 no response, no clue. Other development boards with CP2102, always working for more than 6 years, so we would conclude this extends, the problem persisted with those M5Stack Core2 for AWS. DTR / RTS auto reset signal looks pretty the same as before, but serial response nothing, esptool prompts for timeout. M5burner is just a fancy wrapper with esptool encapsulated, and of course, the same report of timeout and no burn.
here is simple procedure for the test and hosted open source code, https://github.com/xiaolaba/ESP32_AWS_IoT_EduKit_quick_test