@Rick: The package has been received and the unit has been checked. To me it seems something on the SPI bus is interfering with the microcontroller. I took the microcontroller out, put it in a standalone chip programmer, and re-flashed bootloader to it. After that, I popped it back in and was able to upload firmware from the USB port. It’s not clear to me what was the original cause. It could be a soldering related issue, since this is a DIY kit, it could be a flash memory corruption issue. In any case, you will receive an email to arrange for return shipping.