There are calls that enter the queue, but are not heard or after a few seconds they end automatically.
They are only some calls, it does not happen in all.
I have taken an image that I put below:
At the top, the call with incidence.
At the bottom, an OK call.
I see that the first 5 lines of the trace are the same. But then, on the sixth line, the incident call makes an APP_END