The develop option UseHeavyMonitors is only used to set LockingMode=LM_MONITOR. It should probably be removed to avoid inconsistent use.

share/runtime/arguments.cpp: if (UseHeavyMonitors) {
share/runtime/arguments.cpp: "Conflicting -XX:+UseHeavyMonitors and -XX:LockingMode=%d flags\n", LockingMode);
share/runtime/globals.hpp: develop(bool, UseHeavyMonitors, false, \
share/runtime/globals.hpp: "+UseHeavyMonitors") \

  if (UseHeavyMonitors) {
    if (FLAG_IS_CMDLINE(LockingMode) && LockingMode != LM_MONITOR) {
      jio_fprintf(defaultStream::error_stream(),
                  "Conflicting -XX:+UseHeavyMonitors and -XX:LockingMode=%d flags\n", LockingMode);
      return false;
    }
    FLAG_SET_CMDLINE(LockingMode, LM_MONITOR);
  }

It's not found in any of the hotspot tests. But there are two instances in the jdk tests:

grep -r UseHeavyMonitors
jdk/java/lang/Thread/virtual/CarrierThreadWaits.java: * @run junit/othervm -XX:+UseHeavyMonitors CarrierThreadWaits
jdk/java/util/concurrent/ConcurrentHashMap/MapLoops.java: * @run main/othervm/timeout=1600 -XX:+UseHeavyMonitors -XX:+VerifyHeavyMonitors MapLoops