clean_up_interfaces_response in lib/facter/resolvers/networking.rb only handles the IPv4 case "10.16.132.213 --> 10.16.132.213", but it should also cases where IPv6 is being used (2001:db8:cafe::132:213 --> 2001:db8:cafe::132:213)
Symptom
Jun 18 19:09:59 host puppet-agent[3958]: (Facter) invalid address: 2001:db8:cafe::213:1001:db8:cafe::213:2