Event Hub receiver does not read all messages

Question

I implemented 2 simple services in Service Fabric, which communicate over Event Hub and I encounter very strange behavior.

The listener service reads the messages using PartitionReciever with ReceiveAsync method. It reads the messages always from the start of the partition, but even though the maxMessageCount parameter is set to very high number, which definitely exceeds the number of messages in the partition, it reads only "random" amount of messages but never the full list. It always starts to read correctly from the beginning of the partition but it almost never reads the full list of messages which should be present there...

Did I miss something in documentation and this is normal behavior, or am I right, that this is very strange bahviour?

A code snippet of my receiver service:

PartitionReceiver receiver = eventHubClient.CreateReceiver(PartitionReceiver.DefaultConsumerGroupName, Convert.ToString(partition), PartitionReceiver.StartOfStream);

ServiceEventSource.Current.Write("RecieveStart");
IEnumerable<EventData> ehEvents = null;
int i = 0;
do
{
    try
    {
        ehEvents = await receiver.ReceiveAsync(1000);
        break;
    }
    catch (OperationCanceledException)
    {    
        if (i == NUM_OF_RETRIES-1)
        {
            await eventHubClient.CloseAsync();
            StatusCode(500);
        }
    }
    i++;
} while (i < NUM_OF_RETRIES);