I have 2 unraid servers running ddclient, and I have the same error on both, turned on verbose
WARNING: '' is not a valid IPv4 or IPv6 address
WARNING: found neither IPv4 nor IPv6 address
WARNING: unraid: unable to determine IP address with strategy use=ip
WARNING: Could not determine an IP for unraid
Both are set up to push IP to namecheap and both are behind Ubiquiti router. Have not made any changes recently and it was working for several months flawlessly.