When JVM waits on a class loading lock, JVMTI_EVENT_MONITOR_WAITED is posted, but the corresponding JVMTI_EVENT_MONITOR_WAIT is not.

Though JVMTI Spec does not strictly prescribe when these events should occur (see JDK-6455295), the common sense suggests that whenever an object waiting happens either both events should be posted or none at all.

Here is an example to demonstrate the issue:
(java -agentlib:monitorWaitAgent MonitorWait)

// MonitorWait.java
public class MonitorWait {
    
    public static void main(String[] args) {
        new Thread(Parent::new).start();
        new Child();
    }
 
    static class Parent {
        static {
            try {
                Thread.sleep(200);
            } catch (Exception e) { /* ignore */ }
        }
    }

    static class Child extends Parent {
    }
}

// monitorWaitAgent.c
#include <jvmti.h>
#include <string.h>
#include <stdio.h>

void JNICALL MonitorWait(jvmtiEnv* jvmti, JNIEnv* env, jthread thread, jobject object, jlong timeout) {
    printf("> MonitorWait\n");
}

void JNICALL MonitorWaited(jvmtiEnv* jvmti, JNIEnv* env, jthread thread, jobject object, jboolean timed_out) {
    printf("< MonitorWaited\n");
}

JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* vm, char* options, void* reserved) {
    jvmtiEnv* jvmti;
    jvmtiEventCallbacks callbacks;
    jvmtiCapabilities capabilities;

    (*vm)->GetEnv(vm, (void**)&jvmti, JVMTI_VERSION_1_2);

    memset(&capabilities, 0, sizeof(capabilities));
    capabilities.can_generate_monitor_events = 1;
    (*jvmti)->AddCapabilities(jvmti, &capabilities);

    memset(&callbacks, 0, sizeof(callbacks));
    callbacks.MonitorWait = MonitorWait;
    callbacks.MonitorWaited = MonitorWaited;
    (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
    (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_MONITOR_WAIT, NULL);
    (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_MONITOR_WAITED, NULL);
    
    printf("Agent loaded\n");
    return 0;
}