esaProbeHistorySeqGaps is a 64-bit performance counter counting sequence-number gaps of two or more across received packets, for a completed interval that has already closed and been archived into the rolling history log; it does not apply to Y.1731 probes. A sequence gap is an early-warning proxy for packet loss, showing up the moment a packet fails to arrive, so a technician can correlate it against the direct loss counters recorded in the same bin. For example, an archived bin showing sequence gaps but no matching lost-packet count would flag a counter-logic anomaly worth reporting, rather than genuine packet loss that night.