I checked first if this was a general Woocommerce problem, but it wasn't.
Google Search Console gives an error because of changes in their policy of reviews (and how the review snippets should be coded).
Google has decided to alter its review system to prevent “selfmade reviews” to be made. Therefore, reviews have to be tied to specific products, courses, books, etc.
Now are all separate reviews layered under a “review” within a review, which makes it logical for Google to perceive it as a self-fulfilling review.
Review with Ratings example:
https://developers.google.com/search/docs/data-types/review-snippet
There are 2 suggestions:
- We suggest the “reviews” in the theme are bundled as “reviewRating”s under 1 @type review.
- Completely remove the markup on separate reviews; as Google mentions it only uses the aggregate review component:
https://developers.google.com/search/docs/data-types/product