The cause is around https://github.com/xwiki-contrib/book-versions/blob/c81acdd94aa054388e27d1e6d908e12f05406376/application-book-versions-api/src/main/java/org/xwiki/contrib/bookversions/internal/PublishBookRightInitializer.java#L89 and it is related to the fact that every Right has a value, and that value needs to be below 64 because of the way we store right sets. And when you unregister a right that is not the last registered right, you break that whole system. So, basically, unregistering of rights is only supported when you unregister the last registered right. Plus, the values that are associated with rights need to be continuous.
