Google said that as of May 10, 2021, it changed the way it reports on certain structured event data.
Specifically, Google will now start to detect event entities at all hierarchical levels (not just the root level), and errors in recommended attributes will now be marked as warnings instead of errors.
Google added that Google Search Console “has changed the way that it evaluates and reports errors in Event structured data.”
The company stated that this may cause you to see “a slight increase in the number of entity incidents and problems reported for your property, as well as changes in the severity of certain problems, from errors to warnings.”
Here is how event structured data rich results can appear in Google Search: