The example workflow submitted by users was failing with the below ClassNotFound exceptions
java.lang.RuntimeException: java.lang.ClassNotFoundException: Class org.apache.oozie.example.SampleMapper not found
ROOT CAUSE :
These classes are found in oozie-examples-<version>.jar file, which is expected to be present in the lib folder of the job.
Add the oozie-examples-<version>.jar file to the lib folder of the job and then submit the job.