The output contains:

# ERROR: Some MyThreads were killed. nsk.jdb.kill.kill001.kill001a.notKilled = 4 remaining
The following stacktrace is for failure analysis.
nsk.share.TestFailure: Some MyThreads were killed. nsk.jdb.kill.kill001.kill001a.notKilled = 4 remaining
at nsk.share.Log.logExceptionForFailureAnalysis(Log.java:432)
at nsk.share.Log.complain(Log.java:403)
at nsk.jdb.kill.kill001.kill001.runCases(kill001.java:154)
at nsk.share.jdb.JdbTest.runTest(JdbTest.java:149)
at nsk.jdb.kill.kill001.kill001.run(kill001.java:81)
at nsk.jdb.kill.kill001.kill001.main(kill001.java:75)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:577)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:142)
at java.base/java.lang.VirtualThread.run(VirtualThread.java:293)
at java.base/java.lang.VirtualThread$VThreadContinuation.lambda$new$0(VirtualThread.java:178)
at java.base/jdk.internal.vm.Continuation.enter0(Continuation.java:343)
at java.base/jdk.internal.vm.Continuation.enter(Continuation.java:336)

Note there should still be 5 MyThreads, but the output says only 4 are left. The issue seems to be the following:

        // Sleep during waitTime to give debugger a chance to kill debugee's thread.
        // Note vthreads need a short sleep because they will never receive the kill,
        // and therefore sleep the full time, resulting in a test timeout if too long.
        try {
            Thread.currentThread().sleep(kill001a.vthreadMode ? 1000 : kill001a.waitTime);
        } catch (InterruptedException e) {

1000ms is much too short, so during some runs the vthread is exiting sleep before the test has had a chance to verify that the thread is still alive after having issued the kill command. Note the kill command is expected to fail for vthreads and will not terminate the thread, so after the kill is done for all 5 threads, they should still all be alive for a short while (until the sleep times out).

The sleep needs to be longer, but we don't want it to be too long because the test always needs to wait until the sleep completes. 20 seconds should be reasonable.