Basic parallel processing doesn't work!

Version: camunda-bpm-tomcat-7.10.0

I created a simple model with parallel tasks inside which does nothing other than printing a statement. When I run the process, I get org.camunda.bpm.engine.OptimisticLockingException: ENGINE-03005 Execution of 'UPDATE ExecutionEntity[9fef7f01-6133-11e9-b942-acde48001122]' failed. Entity was updated by another transaction concurrently.


Am I doing anything wrong?