Maybe you can try to wipe the whole flash : esptool.py --port /dev/ttyUSB0 erase_flash
Otherwise, maybe your Arduino IDE installation has a problem and/or your ESP module itself (do you have spares ?)
We have a POST request.
IO: 16 HIGH
webserver's 192.168.4.100:59921 err -9 reconnect
We have a POST request.
IO: 16 LOW
webserver's 192.168.4.100:52874 err -9 reconnect
T:2,bf0,-2
We have a POST request.
IO: 16 HIGH
webserver's 192.168.4.100:58702 err -9 reconnect
We have a POST request.
IO: 16 LOW
webserver's 192.168.4.100:41475 err -9 reconnect
We have a POST request.
IO: 2 LOW
webserver's 192.168.4.100:50476 err -9 reconnect
Meaning that the board is working with IOT.bin firmware.