This counts the number of times a received FCIP Special Frame carried an invalid nonce -- a one-time value used during the handshake to prevent replay or connection confusion -- on this link. A climbing count here suggests either a stale or duplicate handshake attempt being received, perhaps from a flapping connection retry, or in a worst case, unexpected connection attempts, either of which merits investigation distinct from a simple connectivity failure. Repeated invalid-nonce events on a link that otherwise looks stable could indicate an old, already-superseded connection attempt from the remote side lingering and retrying against stale handshake state.