What would cause incoming external calls to stop going to voicemail, requiring a UC540 to be power-cycled to restore that functionality. The UC540 is configured with inbound sip trunks which all are sent to a blast group with 30 second timeout and a no-answer forward to 401. All phones in the blast group have a 35 second timeout. This works fine for a while, often several days, but then unanswered inbound calls stop going to voicemail after 30 seconds and the caller just hears continued ringing. The blast group phones stop showing the incoming call after 30 seconds, but it never gets routed to voicemail. Voicemail is working, however, for internal calls, and there seems to be no communication issue with CME contacting CUE using the configured IP addresses. So far, the only cure I've found for this issue is to power-cycle the UC540, which, needless to say, is very disruptive.