These 3 lines are the uplink, RX1 (one second after the uplink was done) and RX2 (2 seconds after the uplink was done).
Now, assuming the timestamps (actually: ticks) are printed right before the action is being executed, a bit of math: 6,058,840 - 5,996,920 = 61,920, so 1 second between RX1 and RX2 is 61,920 ticks. Also, 5,996,920 - 5,931,266 = 65,654, in which an uplink with 2 bytes of application payload at SF7 takes about 46.3 ms, so here 1.0463 seconds = 65,654, hence converting back to one second yields 62,748 ticks? Those variations might make it hard for the device to be listening at the exact time that a gateway might be transmitting the downlink.
To mitigate that, see MAX_CLOCK_ERROR.