Hibernate 5.0.0.CR4 has introduced a change in default ImplicitNamingStrategy (https://github.com/hibernate/hibernate-orm/releases/tag/5.0.0.CR4).

Existing applications using default naming strategy can now experience a crash due to invalid SQL queries generated.

See https://issues.jboss.org/browse/KEYCLOAK-1777 for more details, and for a work-around.