This counter counts instances where a UNI (User-Network Interface) message arrived with a sequence number that didn't match what was expected. An administrator treats a rising count as a sign of signaling desynchronization between the switch and the attached device, which can eventually cause the LMI session to be declared down. For example, after a brief outage on a UNI link, an engineer might see this counter increment as the two sides briefly disagree on sequence numbers before resynchronizing.