Corporates. At work your network is IPv4 only, it passes through a badly made "anti-exfiltration" appliance, a "policy enforcement" appliance and half a dozen more, you have that six year old laptop that's missing some crucial patches because they were incompatible with the Java applet used to order coffee in the board room, and so on.
At home you've been using IPv6 passively for 18 months, it works and you never noticed.
Hence the big up spike on weekends and major holidays.
It's on a weekly cycle, with peaks presumably on the weekends. Maybe more home internet connections than workspace internet connections are IPv6, so there is an uptick in registered IPv6 connections when people are at home. (Note how the trough between Dec 24th and 31st is also significantly more shallow than the usual one.)
