Start of using jdk11 instead of jdk8 introduced random failure in JBPM performance tests. One of the failures can be seen in build 8. NullPointerException was raised in LParallelGatewayTwoTimesProcess test running with multiple threads. 

It seems that initialization of KieSession in single thread init() method fixed the issue. I believe that problem might be caused by creating of ProcessVariableIndexers not being thread safe.