Job is executed twice despite DisableConcurrentExecution

public async Task ProcessPicking(HttpRequest incomingRequest)
{
    var filePath = await StoreStreamAsync(incomingRequest, TriggerTypes.Picking);
    var picking = await XmlHelper.DeserializeFileAsync<Picking>(filePath);
    // delay with 20 minutes so outbound-out gets the chance to be send first
    BackgroundJob.Schedule(() => StartPicking(picking), TimeSpan.FromMinutes(20));
}

[TriggerAlarming("[IMPORTANT] Failed to parse picking message to **** object.")]
[DisableConcurrentExecution(30)]
public void StartPicking(Picking picking)
{
    var orderlinePickModels = picking.ToSalesOrderlinePickQuantityRequests().ToList();
    var orderlineStatusModels = orderlinePickModels.ToSalesOrderlineStatusRequests().ToList();

    var isParsed = DateTime.TryParse(picking.Order.UnloadingDate, out var unloadingDate);

    for (var i = 0; i < orderlinePickModels.Count; i++)
    {
        // prevents bugs with usage of i in the background jobs
        var index = i;
        var id = BackgroundJob.Enqueue(() => SendSalesOrderlinePickQuantityRequest(orderlinePickModels[index], picking.EdiReference));
        BackgroundJob.ContinueJobWith(id, () => SendSalesOrderlineStatusRequest(
        orderlineStatusModels.First(x=>x.SalesOrderlineId== orderlinePickModels[index].OrderlineId), 
        picking.EdiReference, picking.Order.PrimaryReference, isParsed ? unloadingDate : DateTime.MinValue));
    }
}

[TriggerAlarming("[IMPORTANT] Failed to send order line pick quantity request to ****.")]
[AutomaticRetry(Attempts = 2)]
[DisableConcurrentExecution(30)]
public void SendSalesOrderlinePickQuantityRequest(SalesOrderlinePickQuantityRequest request, string ediReference)
{
    var audit = new AuditPostModel
    {
        Description = $"Finished job to send order line pick quantity request for item {request.Itemcode}, part of ediReference {ediReference}.",
        Object = request,
        Type = AuditTypes.SalesOrderlinePickQuantity
    };

    try
    {
        _logger.LogInformation($"Started job to send order line pick quantity request for item {request.Itemcode}.");
                
        var response = _service.SendSalesOrderLinePickQuantity(request).GetAwaiter().GetResult();
        audit.StatusCode = (int)response.StatusCode;
        if (!response.IsSuccessStatusCode) throw new TriggerRequestFailedException();
                
        audit.IsSuccessful = true;
        _logger.LogInformation("Successfully posted sales order line pick quantity request to ***** endpoint.");
    }
    finally
    {
        Audit(audit);
    }
}