Our reception phones have three appearance buttons to handle incoming calls. When they are on the phone and another call comes in they used to see the call on the 2nd appearance button, put the first call on hold, then pickup the second call. Lately the second appearance button will not alert them for new calls coming in. They can hear the phones ringing at other extensions so they put their current call on hold and have to wait about a ring or two before the call appears on their phone. Is there a setting that could cause this to happen?