AVAYA IPO 500 v9.0.316.2 with 5 SIP trunks.

Mobile twinning is set up on 101, so incoming call will ring group 200 (including 101,102,103), as well as an external mobile number.

when we turn twinning on 101, it looks all right at first. After a couple of calls, twinning will stop working, the button shows twinning is still in progress, and when we look at "system status", 2 SIP trunks are still "connected", one is for incoming, the other is for outgoing to twinned mobile.

Called for tech support, they said settings in phone system were right, suggested to upgrade to 9.0.12

Anyone knows why this happens, and any suggestions?