EF Core - duplicate error when adding entities

When adding entities to a DbContext in EF Core I get following error message:

The instance of entity type 'OrderTask' cannot be tracked because another instance with the key value '{Id: 1}' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

Indicating I have multiple entities with the same Id (Id:1). But this is not the case.
Any suggestions on the source of this error or how to debug it would be appreciated.

Database

CREATE TABLE "Tasks" (
	"Id"	INTEGER NOT NULL,
	"Description"	TEXT NOT NULL,
	CONSTRAINT "PK_Tasks" PRIMARY KEY("Id" AUTOINCREMENT)
);

Entity

public class OrderTask : BaseEntity<int>
{
    public string Description { get; set; }
    public ICollection<Machine> Machines { get; set; }
}

public class BaseEntity<T> where T : struct
{
    public T Id { get; set; }
}

Adapter

public async Task AddOrUpdateTasks()
{
    using var cn = new SqlConnection(_cn);
    await cn.OpenAsync();
    var cmd = new SqlCommand();
    cmd.CommandType = System.Data.CommandType.StoredProcedure;
    cmd.CommandText = "usp_Task_Sel_All";
    cmd.Connection = cn;

    using var dr = await cmd.ExecuteReaderAsync();
    while (await dr.ReadAsync())
        _orderContext.Tasks.Add(new OrderTask() { Id = (int)dr["TaskNumber"], Description = (string)dr["TaskDescription"] });


    await _orderContext.SaveChangesAsync();
}

Method

public async Task EFWorkcenterTest()
{
    var orderContext = new OrderContext();
    orderContext.Database.EnsureDeleted();
    orderContext.Database.EnsureCreated();

    var adapter = new Adapter(orderContext);
    await adapter.AddOrUpdateTasks();
}

I already tried checking for duplicates with

var dup = _orderContext.Tasks.GroupBy(x => x.Id)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToList();

but this returned 0.

Explicitly setting the key also did not help.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<OrderTask>()
        .HasKey(x => x.Id);          
}

Removing AUTOINCREMENT on the table did it!
Since the first entry from the SqlCommand returned Id = 0, EF Core or SQLite assigned it the value 1. So after this point there were two duplicate entries.

Thanks to @MikeMozhaev!