Arduino Nano ch340 flashing Troubleshooting

Today, some weird things happened.

All of my arduino nano weren't flashed!

So, I tried to figure out what happened.

it turned out the Arduino IDE 1.8.5 has 2 different version(?) of Processor of ATmega328P

I wasted 1 hour to figure out this.

summary

If you cannot flash copied (CH340) Arduino nano, check the processor.

ATmega328 (Old Bootloader) must be checked!