This counter counts instances where an NNI (Network-to-Network Interface) message arrived with a sequence number mismatch. A rising count signals signaling desynchronization between two network switches connected over an NNI link, which an administrator would want to resolve before it escalates to a link-down condition. For example, an engineer troubleshooting instability on a trunk between two MGX nodes would check this counter for evidence of NNI sequencing problems.