net-dns/pdns-recursor-4.0.0 expects its config file in path /etc/recursor.conf , it seems there is a missing compile time specification to adjust to the old path /etc/powerdns/recursor.conf like former versions. Since the package is installing its shipping config file in the old location as well as older versions do, I consider this a minor glitch due the version bump.
Thanks, fixed with pdns-recursor-4.0.0-r1.