Windows network resource monitor shows active ipv6 connection, but the machine has no ipv6 address

Whilst investigating performance issues on one of our servers (Windows Server 2012) I noticed that the connection with by far the most traffic is to an ipv6 address (ac19:8020::). But according to ipconfig /all, and every setting I can see, this machine has no ipv6 address! So how is this even working? Attempting to ping…