After replacing the built-in cache.conf with the customized file of it from the previous PPM version, an error can be found later in the serverLog pointing to:

Caused by: java.lang.NullPointerException
    at com.microfocus.ppm.webhook.WebHookService.getEnabledWebHooksForEntity(WebHookService.java:158)
    at com.microfocus.ppm.webhook.WebHookService$$FastClassByCGLIB$$9243fc23.invoke(<generated>)
    at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
    at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:700)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
    at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:635)
    at com.microfocus.ppm.webhook.WebHookService$$EnhancerByCGLIB$$b482fba5.getEnabledWebHooksForEntity(<generated>)
    at com.kintana.crt.event.RequestLifecycleEventMgr.queueSaveEvent(RequestLifecycleEventMgr.java:158)
    at com.kintana.crt.web.ctrl.RequestUpdateController.update(RequestUpdateController.java:1220)
    at com.kintana.crt.web.ctrl.RequestUpdateController.update(RequestUpdateController.java:302)
    at org.apache.jsp.web.knta.crt.RequestUpdate_jsp._jspService(RequestUpdate_jsp.java:218)
    ... 85 more

Full article: https://portal.microfocus.com/s/article/KM000017352