Azure Service Bus negative amount of scheduled mes

Question

I need to get a message from queue in some special time. So I use scheduled message in queue. I send messages via ScheduleMessageAsync method.

For getting messages I use Azure Web Job with ServiceBusTrigger.

I send a couple of messages, everything works fine on my side, but in Azure Portal, if I go to page with my queue I see that I have negative amount of messages in queue.

I had this problem some days ago, but then it disappeared, but now appears again.

Is it problem in my logic or just a bug in UI of Azure?

UPD: I had an unhandled exception in my web job, so, it seems like the problem was because of this.

But I still don't know why counter became less than 0