Don't panic. It's not a Google core update, and it's not a bug either. In fact, it's one of the technical guidelines that most site owners often ignored. In Google review snippet guideline, Google says
Pages using LocalBusiness or any other type of Organization structured data are ineligible for the star review feature if the entity being reviewed controls the reviews about itself. For example, a review about entity A is placed on the website of entity A, either directly in their structured data or through an embedded third-party widget.
Put it into plain words, you are not eligible for the star review feature if :
Let's say site A is using Trustpilot and showcasing customer reviews on its page. When you perform a search in Google, you won't see the star review feature displayed in its organic results. However, you will see star review features on websites like its review page on Facebook, productreview.com.au or yelp. So even though site A has a review schema on its website, it's the one being reviewed and controls the reviews. As such, it's ineligible for the star review feature.
In my humble view, many site owners often had the misunderstanding that having a review schema ensures its eligibility for review rich results. Unfortunately, that's not the case anymore. Moreover, I have seen many websites lose their review snippet with no LocalBusiness or any other Organization structured data is being used.
Don't be sad. Google is testing the inclusion of seller ratings in organic search. This feature was previously displayed only in paid search. Seller ratings are an automated extension type that showcases advertisers with high ratings. You have no control over seller rating, but you can make efforts to contribute great, verified reviews to the trusted sources. To be eligible for seller rating, you need to:
To find out if you have a seller rating for a specific country, edit the following URL to replace "www.example.com" with your homepage URL:
Since Google is doing the test, websites can have seller ratings even if they don't buy Google Ads.
Suppose Google doesn't have information for your store or doesn't meet the minimum seller rating thresholds. In that case, a seller rating page may not load for your homepage.
Keep in mind this is just a test, and it appears these are the early stages, according to examples Clark shared on Twitter.