There seems to be two downward rank adjustment early December, adding up to around 0.5k/d downward adjustment. Accumulative ranking adjustment since March 2018 (when OGS conducted a server-wide rank comparison) seems to be around 1.1k/d upward adjustment (i.e 4.0kyu in Mar 2018 is 2.9kyu in Dec 2021).

Ah I was wondering why I was demoted to 2k and didn't manage (yet) to climb back to 1k. Looking at other rank graphs you seem to be correct, other people got demoted as well.

During the month of December 2021, there were a approx. 0.16kyu/dan downward shift, approx. 0.33 kyu/dan downward shift, and approx. 0.5 kyu/dan upward shift in KGS, and we are back to where we were on November 2021.
Accumulated adujustment since March 2018 (when OGS conducted a server-wide survey) is approx. 1.6 kyu/dan upward shift (i.e. 4.0kyu then is the same as 2.4 kyu now.) It also means I have not improved either.