Maybe you cloned the mac address? Try to see it in Interfaces using the web ui or via ssh using the ifconfig | grep HWaddr command on both miners.
Hi.
I understood you are using the SD-method?
In that case if you, like me, have a windows-machine with SD-card reader you can just remove the SD card from the miner, put it into your computer and change the mac addres in uEnv.txt on the SD card with notepad++ or similar.
I used the same mac-adress as my miner had with original FW, but if you have several miners the main thing is that you give each miner a unique mac.
BR.
Steff