Since implementing JPA Hibernate has defined 2 sets of implementations of many of its event listener contracts: one for native behavior, one for JPA-defined behavior. Consolidate this into a single set.
And no words in migration guide about this breaking change. Many people uses JpaIntegrator
I see this one as marked for 6 only. Are you trying 6?
I see this commit in 5.3.1 at least
having integrated JPA and Hibernate listeners the JpaIntegrator is no longer needed.
In case you have a class extending it you should change it to implement the 'org.hibernate.integrator.spi.Integrator'.
Anyway as you suggested we are updating the migration guide in order to include the information about the removal.
Thanks a lot for reporting the issue.