The same happened to me. I use kk star rating plugin and suddenly got the same notification from Google, jsut like @decouvertemonde . The stars in the search result were removed. I am using this plugin as it is and i do not even know what is meant by structured data. Why this kk Star Ratings plugin doesn’t get an update to make it comply with google guidelines?
If you add the code to functions.php, remove this from the beginning:
<?php
