"Six Years After: State of IPv6 Deployment 2018"
https://www.internetsociety.org/blog/2018/06/six-years-after-state-of-ipv6-deployment-2018/
if your instance isn't IPv6 enabled (both inbound and outbound), why the fuck not?
this is a callout post
@nivex its federating over v4 as well which suggests Docker (ugh) or possibly gai.conf address preference change