I'm in Win10 using IDE 1.8.6. I've been successfully uploading code to pro-mini and nano chips maybe 65 times in the last couple weeks. Suddenly the pro-mini uploads work, the nano doesn't. The error I'm getting is:
Using Port : COM4 Using Programmer : arduino Overriding Baud Rate : 115200 avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
All 10 of the "not in sync" responses display in about second, rather than with the usual pause between attempts. I've made sure I'm uploading to "Arduino Nano". I've suspected something on the PCB, so I've attempted the upload to a bare chhip, which has the same symptom.
Serial monitor works fine on this PCB with a Nano.