Event Store Checkpoint Weirdness

Program.cs

using System.Text;
using EventStore.Client;

var settings = EventStoreClientSettings.Create("esdb+discover://localhost:2113?tls=false");
var esClient = new EventStoreClient(settings);

// Give us something to catch up
await WriteEvents(1000);
ulong lastEventPosition = 0;
await CreateSubscription();
await WriteEvents(500, 1000);

async Task CreateSubscription()
{
    var filter = new SubscriptionFilterOptions(
        EventTypeFilter.ExcludeSystemEvents(),
        checkpointReached: (s, p, c) =>
        {
            if (lastEventPosition > p.CommitPosition)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.Write("[OUTDATED?] ");
            }
        
            Console.WriteLine($"Checkpoint reached at {p.CommitPosition}");
        
            Console.ResetColor();

            return Task.CompletedTask;
        });

    await esClient.SubscribeToAllAsync(FromAll.Start,
        (s, e, c) =>
        {
            Console.WriteLine(
                $"{e.Event.EventType} @ {e.Event.Position.CommitPosition}");
        
            lastEventPosition = e.Event.Position.CommitPosition;
        
            return Task.CompletedTask;
        },
        filterOptions: filter);
}

async Task WriteEvents(int numEvents, int msDelay = 0)
{
    for (var i = 0; i < numEvents; i++)
    {
        await esClient.AppendToStreamAsync(Uuid.NewUuid().ToString(), StreamState.Any,
            new[]
            {
                new EventData(Uuid.NewUuid(), "TestEvent", Encoding.UTF8.GetBytes($"{i}"), Encoding.UTF8.GetBytes($"{i}"))
            });

        Console.WriteLine($"Written Event {i}");
        await Task.Delay(msDelay);
    }
}