Google said that starting on May 10, 2021 it has changed how it reports in some event structured data. Specifically, Google will now begin detecting Event entities at all hierarchy levels, not just at the root level, and errors in recommended properties are now flagged as warnings rather than errors.
Google added that Google Search Console “has changed the way that it evaluates and reports errors in Event structured data.”
This may lead to you seeing a “small increases in the number of Event entities and issues reported for your property, as well as a change in severity of some issues from errors to warnings,” the company said.
Here is how event structured data rich results can appear in Google Search:
To learn more about structured data rich results, see this developer doc.
Forum discussion at Twitter.