John
How does the person who has answered a call fron the Yale confirm to the Yale that the call has been answered by a person. ? Is it a PIN that the person dials ?
If it is a PIN then maybe if the same digit sequence is in the number being dialled then the Yale may react to an echo of that digit sequence and assumne the call has been answered even though the diaiing has not been completed and abandon the call. Echo due to impedance mis-match somewhere between auto dialler and the telephone network. ( not uncommon )
try taking the Yale to the direct phone socket.
You will have to turn "Tamper Off" before taking it out of the wall bracket.
I can't see why it should matter, though.
Yale do have a helpline/email desk. It seems to be erratic, it's worked fine for me but I've heard others say they couldn't get through. I haven't heard of this PABX problem before.
Regret I have no knowledge of that PBX.
I would make a high impedance monitor to follow the progress of the call. Various ways to DIY one. The earpiece from a phone in series with a 10,000 Ω resistor and a 0,47 μF capacitor works. Values are not critical other than t capacitor should not be a polarised ( electrolytic ) type.