Bob N0BHC stumbled across an upload problem with an order of 5 Arduino Nanos this week.
This batch of Nanos used the CH340 USB chip and he was certain the USB driver was correct.
He found there had been a recent change in the Arduino IDE (sometime during March ’18) and to program new “old” Nanos you have to select “ATmega328P (OldBootloader)” from the “Tools – Processor:” Menu. After doing this, sketches uploaded to the Nanos just like before.