Here is what Search Engine Land had to say on this:
Google has not officially confirmed any sort of specific update — core
or otherwise. But we know Google is continuously making updates, and
that while it does not confirm each update, it is possible an update
did take place that’s impacting some webmasters, SEOs and site owners.
What we noticed. Over the past several days, especially around January
5 and 6 and January 9, the SEO community within the various online
forums and social media were discussing ranking changes — both
positive and negative ranking changes. While their clients might rank
in position number two on a specific day, the next day, they may have
dropped to position 12 or bumped up to position 1.
Most, but not all, third-party tracking tools that monitor Google
search results have shown significant volatility around the dates
specified above. Here are some screenshots from those tools:
Search engine Land asked Google for a statement about these changes
the community has been noticing. So far, the company has declined to
comment. Google often does not confirm or comment on specific updates
and simply says it continuously makes improvements to search.