Had same problem last night with an RX 470 8gb rig that has been sitting for 3 years.
Dropped in a rx 580 8bg (I thought the 470's were 4gbs')
All cards were bios modded
System recognized only the 580, code 43 on the the 470's
DDU says driver 20.xx.xx was installed for all cards (not the blockchain drivers I was trying to install)
1) unplugged the ethernet cable
2) DDU as administrator
3) Installed blockchain workloads driver from August 11 , 2017 (i am stuck in my ways)
4) Did not reboot
5) Ran AT pixelpatcher as admin (this was the key)
5) Rebooted
all good
I tried a half dozen things last night, gave up and tried the patcher as admin today.
That's one of my big problem on how fixing the error code 43, I almost tried fifferent methods but not luck until today, some say that we need to restore the original bios using the blockchain AMD driver, but I don't think that this will fix the problem. I know that there is a fix for our problem dude.