As indicated the voice port goes down / up several times a day as if someone has administratively shut it down and no one has done so. See attachment.
The NM-HDV-1E1-30E= card and the card in the PBX that this connects to have already been replaced. The next thing left is the 2 metre cable between the router and PBX. Customer ays that there has been no H/W or S/W change in router or PBX before the problem started.