How to perform multiple operations concurrently on DbContext? – Asp.net

I have the following background service running:

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            await Task.Run(async () =>
            {
                while (!stoppingToken.IsCancellationRequested)
                {
                    using (var scope = _scopeFactory.CreateScope())
                    {
                        DataContext dbContext = scope.ServiceProvider.GetRequiredService<DataContext>();
                        var tasks = new List<Task>();
                        tasks.Add(siteA.ProcessSchedule(SportLeagues.MLB, logger, dbContext));
                        tasks.Add(siteB.ProcessSchedule(SportLeagues.MLB, logger, dbContext));
                        //....more of same task
                        await Task.WhenAll(tasks);
                        await dbContext.SaveChangesAsync();
                        await Task.Delay(0, stoppingToken);
                    }
                }
            });
        }

I constantly get this error

System.InvalidOperationException: 
    A second operation was started on this context instance before a previous operation completed.

I can refactor and create a dbContext for each task, however I would prefer to use a single dbContext if possible.

I also tried adding my dbContext as transient:

builder.Services.AddDbContext<DataContext>(options =>
{
    options.UseInMemoryDatabase("db");
}, ServiceLifetime.Transient);

But this did not help. Am I creating my dbContext in an incorrect way? Or is the best approach to create a new dbContext for each task? For more context, this is a constantly running background task, it takes a second to complete and it will have around 20 tasks. It sounds pretty inefficient to be creating and destroying 20 dbContext every second, along with having to do 20 dbContext saves.