This issue grew from my comment in #211 because since making that comment I lost confidence that my issue is related to anybody else's.
Bottom line up front: I think UBIOS_ADDRv4_eth8 was renamed to UBIOS4ALL_ADDRv4_eth8.
I have a Dream Machine Pro UniFi OS 4.0.6.
I use mullvad and wireguard.
Further details are in my next comment.