Looking back over older posts, that reset capability seems to have been added around 1.51 so it would not have worked on 1.42. There is another older post that mentions the same MAC address as you are seeing …..
I suspect that is the MAC address of the lowest level boot function which is all that is active after the hard reset. The above topic suggests that person was going to use TFTP to reload EZSrve. There is no follow-up post to know if that resolved the problem.
I had to use TFTP to reload EZSrve resulting from a problem that came up while using an image that was in test. SHN recommended using SolarWinds free TFTP server download to reload EZSrve. I’ll send you the details in a PM if you are interested in trying that option.