Azure Durable Function doesn't create a storage table entity

I am having a durable function, that I'd like to use to aggregate calculation results as soon as they enter a storage queue. Also, I want the function to create a table entity on an Azure storage table called "result".

The function works as expected, but no single table entity is getting created. However, when I call my test trigger TestTrigger via https://func-foobar.azurewebsites.net/api/create? a table entry gets created.

Why is that? What am I doing wrong here?

namespace Aggregator
{
    public static class AggregatorFunction
    {
        public class ResultEntity
        {
            public string PartitionKey { get; set; }

            public string RowKey { get; set; }

            public uint Run { get; set; }

            public decimal IntermediatePi { get; set; }
        }

        [FunctionName("Counter")]
        [return: Table("result")]
        public static ResultEntity Counter
        (
            [EntityTrigger] IDurableEntityContext ctx,
            ILogger log
        )
        {
            switch (ctx.OperationName.ToLowerInvariant())
            {
                case "add":
                    var unit = ctx.GetInput<UnitOfWork>();
                    log.LogInformation($"Processing: {unit}");

                    (decimal IntermediatePi, ulong IntermediateHits, uint run) = ctx.GetState<(decimal, ulong, uint)>();

                    IntermediateHits += unit.NumHits;
                    IntermediatePi = (decimal)IntermediateHits / unit.TotalRuns * 4.0m;
                    run += 1;

                    log.LogInformation($"==> State: run={run} intermediateHits={IntermediateHits} intermediatePi={IntermediatePi}");
                    ctx.SetState((IntermediatePi, IntermediateHits, run));

                    return new ResultEntity
                    {
                        PartitionKey = "Pi",
                        RowKey = Guid.NewGuid().ToString(),
                        Run = run,
                        IntermediatePi = IntermediatePi
                    };

                case "delete":
                    log.LogInformation("Deleting state!");
                    ctx.DeleteState();

                    return null;
            }

            return null;
        }

        [FunctionName("QueueTrigger")]
        public static async Task Run
        (
            [QueueTrigger(queueName: "results")] string json,
            [DurableClient] IDurableEntityClient entityClient
        )
        {
            var unit = JsonSerializer.Deserialize<UnitOfWork>(json);
            var entityId = new EntityId("Counter", "CounterKey");
            await entityClient.SignalEntityAsync(entityId, "add", unit);
        }

        [FunctionName("HttpResetTrigger")]
        public static async Task Reset
        (
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "reset")] HttpRequest req,
            [DurableClient] IDurableEntityClient entityClient
        )
        {
            var entityId = new EntityId("Counter", "CounterKey");
            await entityClient.SignalEntityAsync(entityId, "delete", null);
        }

        [FunctionName("TestTrigger")]
        [return: Table("result")]
        public static ResultEntity CreateTable
        (
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "create")] HttpRequest req
        )
        {
            return new ResultEntity
            {
                PartitionKey = "Test",
                RowKey = Guid.NewGuid().ToString(),
                Run = 1,
                IntermediatePi = ulong.MaxValue
            };
        }
    }
}