https://vladmihalcea.com/hypersistence-optimizer/docs/user-guide/#BidirectionalSynchronizationEvent
The Hypersistence Optimizer report suggests adding synchronization methods.
When mapping a bidirectional one-to-many or many-to-many association, you need to synchronize both sides of the association. Without synchronizing both sides, Hibernate cannot guarantee that the association state changes propagate to the database.
More, unsynchronized bidirectional associations can also lead to very subtle bugs that are hard to reproduce. For this reason, it’s best to have two utility methods (e.g., addEntity and removeEntity) on the mappedBy side of the one-to-many or many-to-many associations.