After having upgraded the database used by JRM from Oracle 12c to Oracle 19c, logon is impossible.
The error in jrm.log:
[ WARN][localhost-startStop-1] DATE org.hibernate.dialect.resolver.StandardDialectResolver.resolveDialectInternal(): unknown Oracle major version 
[FATAL][localhost-startStop-1] DATE com.levatis.uc4.toolbox.util.HibernateSessionFactory.rebuildSessionFactory(): Error Creating SessionFactory
javax.persistence.PersistenceException: [PersistenceUnit: com.levatis.LRM] Unable to build EntityManagerFactory
Caused by: org.hibernate.HibernateException: Unable to determine Dialect to use [name=Oracle, majorVersion=19]; user must register resolver or explicitly set 'hibernate.dialect'
JRM was not compatible with Oracle 19c until 3.5.1 and superior.
Release : 3.5.0 and inferior
Component : JRM
Oracle 19c has started being supported in JRM 3.5.1 and superior ( currently 3.5.2).
This can be checked in the Compatibility Matrix page:
You will have to either upgrade JRM to 3.5.1+ or downgrade the Oracle database to the previously working version.