esaProbeStatsLostPkts is a 64-bit performance counter counting, combined across both directions, the test packets never received back from the reflector before timeout, for the interval that is still being actively collected (the live bin); it does not apply to Y.1731 probes. This combined figure is the headline number a technician reports against the SLA's packet-loss commitment without manually adding the two directional loss counters together. For example, a technician watching this live total cross the customer's contracted loss threshold mid-interval knows to open a ticket before the bin even finishes closing.