Counts protocol messages received from the peer that arrived out of the expected sequence order. A rising count here suggests message reordering or delay on the inter-chassis link itself (rather than a configuration problem), which an admin would investigate by checking ICL latency, congestion, or a flapping underlying path. A burst of out-of-sequence messages coinciding with a period of ICL congestion would point the admin toward capacity or QoS issues on that inter-chassis link.