MongoDB Java Reactive Streams hangs when performing a query

I’m using the MongoDB Reactive Streams Java API which I implemented following this example, but I’m encountering a serious problem: sometimes, when I try to query a collection, the await methods doesn’t work, and it hangs until the timeout is reached.

The onSubscribe methods gets called correctly, but then neither onNext, nor onError nor onComplete get called.

There doesn’t seem to be a specific circumstance causing this issue.

This is my code

MongoDatabase database = MongoDBConnector.getClient().getDatabase("myDb");
MongoCollection<Document> collection = database.getCollection("myCollection");
FindPublisher<Document> finder = collection.find(Filters.exists("myField"));	
SettingSubscriber tagSub = new SettingSubscriber(finder); 
//SettingsSubscriber is a subclass of ObservableSubscriber which calls publisher.subscribe(this)
tagSub.await(); //this is where it hangs
return tagSub.getWrappedData();