Hangfire executes job twice - asp.net-core

Question

I am using Hangfire.AspNetCore 1.7.17 and Hangfire.MySqlStorage 2.0.3 for software that is currently in production.
Now and then, we get a report of jobs being executed twice, despite the usage of the [DisableConcurrentExecution] attribute with a timeout of 30 seconds.
It seems that as soon as those 30 seconds have passed, another worker picks up that same job again.
The code is fairly straightforward:
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);
}
}
It schedules the main task (StartPicking) that creates the objects required for the two subtasks:
Send picking details to customer
Send statusupdate to customer
The first job is duplicated. Perhaps the second job as well, but this is not important enough to care about as it just concerns a statusupdate. However, the first job causes the customer to think that more items have been picked than in reality.
I would assume that Hangfire updates the state of a job to e.g. in progress, and checks this state before starting a job. Is my time-out on the disabled concurrent execution too low? Is it possible in this scenario that the database connection to update the state takes about 30 seconds (to be fair, it is running on a slow server with ~8GB Ram, 6 vCores) due to which the second worker is already picking up the job again?
Or is this a Hangfire specific issue that must be tackled?