This whole ticketing queue thingy isn't necessarily what it seems. Like everyone else I went through a phase of an inordinate delay to get our flight changes ticketed until I got lucky and happened to have my call answered by a switched-on agent who explained the process to me.
I had thought that ticketing was a completely manual operation where the booking agent transferred the itinerary to a separate ticketing team member who calculated the taxes and issued the ticket, but it turns out that "ticketing" is actually an automated queue.
There are multiple automated queues at any one call centre and I was told that sometimes one of those queues can get stalled for whatever reason (from a technical issue to a simple matter of the booking having faulty sectors that won't allow it to be ticketed), which means that all of the bookings in that queue stop progressing. They can sit there endlessly going nowhere until someone realises that the queue is stalled, and therein lies the real problem - there is no alarm triggered when a queue stalls. Unaware agents may keep adding bookings to a stalled queue and not even realise it is stalled.
Apparently if an agent only takes a cursory look to see if a particular booking is in a queue, they might see it's there and say "oh yes, your booking is in the queue but it hasn't been processed yet". If they don't take the next step to check if the queue is progressing (which I was told, no-one is specifically tasked with doing), then you may call multiple times and get told the same wrong answer multiple times.
In my case the agent said she transferred our booking to another queue and it was ticketed about 12 - 15 hours later.
It's obviously a flawed system.