Cycle race track lap counter

Another issue/detail:

This is the status after tracking 4 transponders for a while:

>Velo.list
={
  "f1:04:79:ec:15:2d random": Velo: {
    id: "A",
    rssi: -78, rssiMin: -98, rssiMax: -57, laps: 42, bat: 65,
    tStart: 1628779258.06911659240, tRssiMax: null, tRssiLast: 1628791487.25615882873, tLastLap: 1628780850.37148475646, tPreviousLap: 1628780823.29253578186,
    rxCount: NaN, state: 0 },
  "dd:16:f9:6a:28:44 random": Velo: {
    id: "B",
    rssi: -65, rssiMin: -96, rssiMax: -57, laps: 44, bat: 78,
    tStart: 1628779258.02102088928, tRssiMax: null, tRssiLast: 1628791487.26290321350, tLastLap: 1628780850.51058387756, tPreviousLap: 1628780823.81463050842,
    rxCount: 11411, state: 0 },
  "f9:2d:30:24:38:a4 random": Velo: {
    id: "C",
    rssi: -65, rssiMin: -97, rssiMax: -63, laps: 57, bat: 100,
    tStart: 1628779258.01436805725, tRssiMax: null, tRssiLast: 1628791487.24501991271, tLastLap: 1628780850.97222328186, tPreviousLap: 1628780823.97481727600,
    rxCount: 27610, state: 0 },
  "e8:44:6b:5f:3e:f0 random": Velo: {
    id: "D",
    rssi: -86, rssiMin: -98, rssiMax: -69, laps: 42, bat: 82,
    tStart: 1628779296.86849403381, tRssiMax: null, tRssiLast: 1628791487.26839637756, tLastLap: 1628780850.93142127990, tPreviousLap: 1628780823.74621009826,
    rxCount: NaN, state: 0 },
  "c2:fc:b0:90:61:c7 random": Velo: {
    id: "E",
    rssi: null, rssiMin: null, rssiMax: null, laps: 0, bat: null,
    tStart: null, tRssiMax: null, tRssiLast: null, tLastLap: null, tPreviousLap: null,
    rxCount: 0, state: 0 },
  "f5:23:d4:cf:c7:8a random": Velo: {
    id: "F",
    rssi: null, rssiMin: null, rssiMax: null, laps: 0, bat: null,
    tStart: null, tRssiMax: null, tRssiLast: null, tLastLap: null, tPreviousLap: null,
    rxCount: 0, state: 0 },
  "c7:da:df:68:c9:fc random": Velo: {
    id: "G",
    rssi: null, rssiMin: null, rssiMax: null, laps: 0, bat: null,
    tStart: null, tRssiMax: null, tRssiLast: null, tLastLap: null, tPreviousLap: null,
    rxCount: 0, state: 0 },
  "d3:8f:95:28:f0:02 random": Velo: {
    id: "H",
    rssi: null, rssiMin: null, rssiMax: null, laps: 0, bat: null,
    tStart: null, tRssiMax: null, tRssiLast: null, tLastLap: null, tPreviousLap: null,
    rxCount: 0, state: 0 }
 }

How can rxCount be set to NaN when this is the only way it is changed in the code:

  this.rxCount = 0;
  this.rxCount += 1;