Hiya, Vivian,
These things seem global, so you probably already know, but if not, here's the status. It appears that the rankings are now doing great and in synch with the reported rankings. Some change frequently, even daily. Others are fixed and don't seem to change at all. Anecdotally, it appears the larger genres change more frequently, and the small ones are frozen. A new wrinkle is that the reads and votes for our book have frozen. Initially, we figured no one was reading it, but after a month, it seems clear we have frozen at 12.6k reads and 2.5k votes. We checked the charts. Adding the number of unique readers should have moved the total, but it appears to be fixed.
Anyway, happy 2019!!
Respectfully,
John and Deb - @ceciandjack