Isn't this showing the percentage of bot traffic from the Yandex IP range?

If so, it isn't particularly surprising that the line would go down.

EDIT: yes, it is. Looking at the same graph for all of Russia, and there's no discernible pattern:

https://radar.cloudflare.com/bots/ru?dateRange=7d

same for the 48h view:

https://radar.cloudflare.com/bots/ru?dateRange=2d