Several webmasters have reported fluctuations on May 1, 2021, and the SERP volatility has also been picked by the tracking tools, giving signs of potential Google update. While details suggest this could be more of development to an earlier update focused on the product reviews, Google said it would not confirm.
For websites working on improving the reviews across their site they may not see the results instantly. Google’s Danny Sullivan has confirmed periodic refresh happening in search results around product reviews, but Google would not post every time when a refresh happens. So, at the moment, websites are expected to continue working towards improving the overall quality of their reviews.