In the past, customers not paying for a static IP were given a /48 IPv6 prefix, and those who were paying would get a /56. 2degrees is currently rolling out a config change which harmonises these configurations, giving everyone a /56.

I just got hit with this, my IPv6 breaking overnight. The fix was simply to change my requested prefix from /48 to /56. All hunky dory again!

Authoritative source: https://www.geekzone.co.nz/forums.asp?forumid=85&topicid=240157

For our dynamic subscribers we allocate a /48 or /56 address space depending on the version of code they are running (due to our currently upgrades in progress), for static customers we allocate a /56 address space. Upgrades are planned to be completed in the first week of November 2018 which will see us standardise on /56 for all subscribers.