In 2.8.2 a new argument, config, was added to the ThrowablePatternConverter constructor without adding a constructor with the original signature specifying a default value. This breaks backwards compatibility with third party subclasses. If no external subclassing was intended, the constructor should have been made package private instead of protected.
This is not just a theoretical problem. For example, it is annoying when using Spring Boot and wanting to use a newer Log4j2 than the default 2.7 because Spring Boot has its own ExtendedWhitespaceThrowablePatternConverter. The system does not crash but the log gets some NoSuchMethodError exceptions.