Google has updated its review snippet structured data guidelines to say the author name of the reviewer must be less than a 100 characters. If it is longer than 100 characters your page won’t be eligible for an author-based review snippet, Google said.
You can find the update to the docs over here where Google wrote under the author property “The reviewer’s name must be a valid name. For example, “50% off until Saturday” is not a valid name for a reviewer.”
Google added here “This field must be shorter than 100 characters. If it’s longer than 100 characters, your page won’t be eligible for an author-based review snippet.”
I guess Google is seeing spammy long names being used in the author name fields as a way to maybe influence and trigger a higher click through rate from the search results?
Forum discussion at Twitter.