Why can I not access class variables from onComplete in Flow API Subscriber

Using the Java Flow API. I have a chain of Processors and a terminal Subscriber. I have coded up Subscribers that have kept a count of items received that work fine with a SubmissionPublisher.

However, when I pass values on from a Processor (which extends SubmissionPublisher) to the Subscriber below, no output is printed to the console.

If I remove minValue.get() the text is printed to the console. Why does the calling class variable cause onComplete not to execute as expected?

public class MinValue implements Subscriber<Integer> {

    private Flow.Subscription subscription;
    private AtomicInteger minValue=new AtomicInteger(Integer.MAX_VALUE);

    @Override
    public void onSubscribe(Flow.Subscription subscription) {
        this.subscription = subscription;
        subscription.request(1);
    }

    @Override
    public void onNext(Integer item) {
        if(minValue.get()>item){
            System.out.println("Min Value : "+item);
            minValue.set(item);
        }
        subscription.request(1);
    }

    @Override
    public void onError(Throwable throwable) {
        System.out.println("Error  + throwable.getMessage() \nMin Value is : "+minValue.get());
    }

    @Override
    public void onComplete() {
        System.out.println("Successful Completion  - Min Value is : "+minValue.get());
    }
}

Edit - adding Minimal Reproduceable Example

   public class NewClass {
           public static void main(String args[]) {
           SubmissionPublisher<Integer> publisher = new SubmissionPublisher<>();
           Subscriber<Integer> subscriber = new MinValue();

           publisher.subscribe(subscriber);
  
           publisher.submit(10);
           publisher.submit(11);
           publisher.submit(9);
           publisher.submit(12);
           publisher.submit(8);

           publisher.close();
       }
   }

The issue was that the main thread was exiting before the subscribers onComplete() was called.

If I add a sleep after calling publisher.close() the subscriber.onComplete() gets time to execute on its own thread.