esaProbeStatsR2PLostPkts is a 64-bit performance counter counting test packets sent from the reflector back to the probe that never came back before the configured timeout, for the interval that is still being actively collected (the live bin); for Y.1731 probes these are actual lost data frames rather than timed-out test packets. Because loss is broken out by direction, a technician can tell which leg of the circuit is actually dropping traffic instead of only knowing that loss happened somewhere on the round trip. For example, if this live counter climbs while the opposite-direction loss counter stays at zero, the technician immediately knows to focus the live troubleshooting on the return leg of the path.