RESOLVED - I have searched pega community forum for similar issue and did not find any. So thought of sharing the root cause for other members reference.

Issue: Pega 8.4.4 instance running in tomcat7 oracle 19c upgraded from Pega 7.2.2. Failed to start and received  ClassNotFoundException  com.hazelcast.config.InvalidConfigurationException. Even though there is no such class in any of the hazelcast jar in pr_engineclasses table we were unable to find any solution for a while. we were looking for possbile hazelcast miss configuration based on java trace detail Caused by: java.lang.ClassNotFoundException: com.hazelcast.config.InvalidConfigurationException

Root cause : This error was due to missing tomcat work (work\catalina\localhost) directory where tomcat extracts the prweb.war file during startup.

Fix: Created tomcat work directory structure with necessary file permissions. Resolved the issue and able to start Pega 8.4.4 instance successfully

REF: tomcat catalina.log 

=============== End Bootstrap Configuration ===============

05-Nov-2021 16:57:18.986 SEVERE [main] com.pega.pegarules.internal.bootstrap.PRBootstrap. Problem during method invocation (contextInitialized)
    java.lang.ExceptionInInitializerError
        at com.pega.pegarules.session.internal.engineinterface.etier.impl.EngineStartup.initEngine(EngineStartup.java:389)
        at com.pega.pegarules.session.internal.engineinterface.etier.impl.EngineImpl._initEngine_privact(EngineImpl.java:180)
        at com.pega.pegarules.session.internal.engineinterface.etier.impl.EngineImpl.doStartup(EngineImpl.java:152)
        at com.pega.pegarules.web.servlet.WebAppLifeCycleListener._contextInitialized_privact(WebAppLifeCycleListener.java:210)
        at com.pega.pegarules.web.servlet.AbstractLifeCycleListener._contextInitialized_privact(AbstractLifeCycleListener.java:145)
        at com.pega.pegarules.web.servlet.AbstractLifeCycleListener.contextInitialized(AbstractLifeCycleListener.java:76)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.pega.pegarules.internal.bootstrap.PRBootstrap.invokeMethod(PRBootstrap.java:385)
        at com.pega.pegarules.internal.bootstrap.PRBootstrap.invokeMethodPropagatingThrowable(PRBootstrap.java:427)
        at com.pega.pegarules.boot.internal.extbridge.AppServerBridgeToPega.invokeMethodPropagatingThrowable(AppServerBridgeToPega.java:225)
        at com.pega.pegarules.boot.internal.extbridge.AppServerBridgeToPega.invokeMethod(AppServerBridgeToPega.java:274)
        at com.pega.pegarules.internal.web.servlet.WebAppLifeCycleListenerBoot.contextInitialized(WebAppLifeCycleListenerBoot.java:92)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4678)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5139)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:717)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:690)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:705)
        at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:978)
        at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1848)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
        at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
        at org.apache.catalina.startup.HostConfig.deployWARs(HostConfig.java:773)
        at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:427)
        at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1576)
        at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:309)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:123)
        at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:423)
        at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:366)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:936)
        at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:841)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1384)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1374)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
        at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909)
        at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardService.startInternal(StandardService.java:421)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:930)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:633)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:343)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:474)
    Caused by: java.lang.RuntimeException: Unable to create PRModulesProvider
        at com.pega.pegarules.common.PREngineProvider.<clinit>(PREngineProvider.java:205)
        ... 56 more
    Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.pega.pegarules.common.PREngineProvider.<clinit>(PREngineProvider.java:203)
        ... 56 more
    Caused by: java.lang.: com/hazelcast/config/InvalidConfigurationException
        at com.pega.platform.modules.internal.ModulesBridgeImpl.getModules(ModulesBridgeImpl.java:188)
        at com.pega.platform.modules.internal.ModulesBridgeImpl.<init>(ModulesBridgeImpl.java:167)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
        at java.lang.Class.newInstance(Class.java:442)
        at com.pega.platform.modules.PRModulesProvider.initialize(PRModulesProvider.java:37)
        ... 61 more
    Caused by: java.lang.ClassNotFoundException: com.hazelcast.config.InvalidConfigurationException
        at com.pega.pegarules.internal.bootstrap.phase2.PRBaseLoader.findClass(PRBaseLoader.java:324)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at com.pega.pegarules.internal.bootstrap.phase2.PRBaseLoader.loadClass(PRBaseLoader.java:249)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        at com.pega.pegarules.bootstrap.loader.PRAppLoader.loadClass(PRAppLoader.java:681)
        at com.pega.pegarules.bootstrap.loader.PRAppLoader.loadClass(PRAppLoader.java:550)
        ... 69 more