Some Arduino/clones/serial devices use an optional mechanism (of 802.11 wireless networking protocol) to reduce frame collisions. I don't know why only some devices require it, but I was able to get a Sparkfun Pro Micro atmega32u4 clone to work by adding this line.
jaburns
commented
4 years ago
Some Arduino/clones/serial devices use an optional mechanism (of 802.11 wireless networking protocol) to reduce frame collisions. I don't know why only some devices require it, but I was able to get a Sparkfun Pro Micro atmega32u4 clone to work by adding this line.
I found someone who had a similar problem here: https://www.visualmicro.com/forums/YaBB.pl?num=1531953781