On OSGi container environment (e.g. Karaf), this NoClassDefFoundError will be thrown from pax-logging-log4j2-1.11.2.jar bundle.
In case of there is "JsonLayout" is defined in one log4j2 appender in the log4j configuration.
There was no this problem on the older pax-logging-log4j2-1.10.1.jar bundle, as it has the good MANIFEST defined in the Import-Package for jackson:
Java 8, Java 11