After some tests with the boot loader, and after 'bricking' a TQFP ATMega328p, I've decided not to use the RESET pin as an I/O and the LED was turned into a POWER indicator. The diagram and the board were already updated.

The good news is that the bootloader is working properly and I was able to use it to upload a test firmware for a HID device.

Since the original test platform is still bricked, I am using an ATMega328p borrowed from an Arduino board.