I had the same problem as Antoine: I already owned one ROCK64 board and I just added other 2 (v3.0 2018-1105) and I was having issues with the network. All of them had the same MAC and efuse is empty also.
I flashed the image (Armbian_20.11.3_Rock64_focal_current_5.9.14_desktop in my case) on the eMMC and then I modified /etc/network/interfaces before starting for the first time, and all worked like a charm.
I usually modify also the hostnames, so the avahi announce on the network is different for each board.
Neurone got a reaction from FossCoder in Rock64 - same mac on two boards