Google seems to have fixed the bug where review snippets were not displaying in Google Search.
Timeline. The bug began creeping into the Google Search results interface on Wednesday, July 21st based on the reports that were sent to us. By the following day, Thursday, July 22nd, the review starts were hard to find for any query you conducted in Google. Google confirmed the issue on Friday, July 23rd. Then yesterday afternoon, Monday, July 26th, the issue started to get resolved where now everyone seems to be able to see review stars in the Google Search results.
Reporting issues. Google also wrote on the data anomalies page that between July 19th and 23rd in the Google Search Console Performance reports for Google Search, “Due to an internal issue, you may see a drop in your Review snippet and Product rich results performance during this period. We regret any problems this may have caused on your site.” So make sure to annotate your own internal reports about this issue.
Why we care. Google was not showing review stars in the search results and that can lead to a lower click through rate from the search results. Lower click through rates can lead to less traffic and less traffic can lead to less conversions. But at the same time, your competitors likely did not show the review stars, so everyone was in the same boat.