If you put NONE into the MAC Address section then the code see’s that it is not blank and checks that it is a valid mac address. NONE is not a valid mac address hence you get the error message.
That has not changed since at least 2014. I went back to the Core Update 60 code (10 years ago) and the above checks are the same now as then. Also checked the validmac function in the general-functions.pl code from that same CU version and it has also not changed.
So I can’t see how it would have worked with NONE in the MAC address in the past unless some changes occurred at some time in the past and were then reverted at a later CU.
Can you test and confirm with an earlier CU version and let me know the version number then I could install it on my VM testbed and see if I can reproduce it and check out the code for that version.