Google pubsub listener not receiving all the messages - google-cloud-storage

Question

I'm using Google Cloud Storage for storing objects, with the bucket associated to a topic and subscription id. The flow is such that a Java application requests for the upload link(s), and upload object(s) using those upload link(s). I also have a pubsub listener implemented in Java, which receives the upload notification message, and does something on every successful upload. This is the snippet that handles the event listening.
public void eventListener() {
MessageReceiver messageReceiver = (message, consumer) -> {
final Map<String, Object> uploadMetaDataMap = getUploadDataMap(message);
LOGGER.info("Upload event detected => {} ", uploadMetaDataMap);
// do something
consumer.ack();
};
Subscriber subscriber = null;
Subscriber finalSubscriber = subscriber;
/* To ensure that any messages already being handled by receiveMessage run to completion */
Runtime.getRuntime().addShutdownHook(new Thread() {
#Override
public void run() {
finalSubscriber.stopAsync().awaitTerminated();
}
});
try {
subscriber = Subscriber.newBuilder(subscription, messageReceiver)
.setCredentialsProvider(FixedCredentialsProvider.create(creds)).build();
subscriber.addListener(new Subscriber.Listener() {
#Override
public void failed(Subscriber.State from, Throwable failure) {
// Handle failure. This is called when the Subscriber encountered a fatal error and is shutting down.
LOGGER.error(String.valueOf(failure));
}
}, MoreExecutors.directExecutor());
subscriber.startAsync().awaitRunning();
subscriber.awaitTerminated();
} finally {
if (subscriber != null) {
subscriber.stopAsync().awaitTerminated();
}
}
}
I'm storing the objects in this format => bucket/uuid/objectName.extension and on every successful upload, LOGGER.info("Upload event detected => {} ", uploadMetaDataMap); logs messages like this
2020-08-03 16:12:14,686 [Gax-1] INFO listener.AsynchronousPull - Upload event detected => {size=85, uuid=6dff9a20-3995-4f28-93e9-79e6c3cf613d, bucket=bucketName}
The issue I'm facing now is, not all the successful upload events send out notification message. I can see the folder structure created in the GCS with the respective object inside it, but notification related to that upload is nowhere to be found in the logs printed by pubsub listener. It's been bothering me for a while now, and could really use some help with this.