The circuit between you and your remote office could be DACS'd across several SONET rings between point A and B and if the cut took out one of those rings then you'd lose your circuit. Also, keep in mind that carriers love to call SONET rings redundant even when both the working and protect sides of it ride in the same conduit, or hell, even in the same buffer. That makes them a little more susceptible to backhoe fade. There are other possibilities as well, such as the protect side of the ring being down for maintenance when something hits the working side, the carrier screws up a re-groom, etc...
jms