Third-party tools and rank trackers are showing fluctuations with the epicenter being October 22nd 2020.
If accurate, this comes almost a month to the day that Yandex Webmaster tools distributed a message that:
Technical work is being carried out aimed at expanding the search base. They can lead to temporary changes in the number of pages in the search base. We do not expect significant changes in search traffic to sites in this regard.
Forum chatter for the 22nd is low, however, some webmasters are sharing news of ranking reversals in the days leading up to the 22nd, in comparison to the same time in September.
As more information comes to light, we will update.