IDE 220.127.116.11, Windows 10.
I bought 4x new Arduino Uno's to flash together with the same project.
Brand new, never touched, out of the box 1, 2, 3 all flash right away and we're up and running.
The 4th doesn't enumerate in Windows device manager at all. I grabbed my Atmel-ICE and plugged into the ISP port and fired up Microchip studio - sure enough the MCU checks out and looks fine.
I checked the application MCU as well and that also appears to be alive.
I grabbed the Uno DFU and serial hex file from the github project here, and installed the hex file using Microchip studio. I also program the fuses in line with their recommendations to the Atmega16U2 based on the github readme. Everything flashes and reads back fine.
Now I plug my Uno back in via USB and sure enough it shows up in the Arduino IDE - great!
I can query board info and get a response back:
BN: Arduino Uno
Looks good to me.
I go and click program with the same application as before, and all I get are these errors:
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x55
I've restarted my computer, reset the Arduino, reinstalled drivers, restarted the IDE, used different USB ports, etc etc on and on.
Is this likely just a board that shouldn't have left the factory? Some unseen hardware issue with the Uno?