Time of the previously acked packet is larger than the ack time of the current packet

[kinokrt]

In bandwidth_sampler.cc, within OnPacketAcknowledgedInner, the following ERROR is logged. Could you please explain in detail why this is possible? Additionally, I noticed a TODO in the code—is it related to this issue? Could you please describe all potential causes that might trigger this?

  // During the slope calculation, ensure that ack time of the current packet is
  // always larger than the time of the previous packet, otherwise division by
  // zero or integer underflow can occur.
  if (ack_time <= a0.ack_time) {
    // TODO(wub): Compare this code count before and after fixing clock jitter
    // issue.
    if (a0.ack_time == sent_packet.sent_time()) {
      // This is the 1st packet after quiescense.
      QUIC_CODE_COUNT_N(quic_prev_ack_time_larger_than_current_ack_time, 1, 2);
    } else {
      QUIC_CODE_COUNT_N(quic_prev_ack_time_larger_than_current_ack_time, 2, 2);
    }
    QUIC_LOG_EVERY_N_SEC(ERROR, 60)
        << "Time of the previously acked packet:"
        << a0.ack_time.ToDebuggingValue()
        << " is larger than the ack time of the current packet:"
        << ack_time.ToDebuggingValue()
        << ". acked packet number:" << packet_number
        << ", total_bytes_acked_:" << total_bytes_acked_
        << ", overestimate_avoidance_:" << overestimate_avoidance_
        << ", sent_packet:" << sent_packet;
    return BandwidthSample();
  }