B1: autoreset after a few minutes, how to debug

var ACC = 1;
var MAG = 2;
var GPS = 3;
var TIM = 4;

var bufs = [];
var buf = new ArrayBuffer(1000);
var bufi = 0;

function get_dv(len) {
  if (buf.length < (bufi + len)) {
    buf[bufi] = 0;
    bufs.push(buf);
    buf = new ArrayBuffer(1000);
    bufi = 0;
  }
  var dv = new DataView(buf, bufi);
  bufi += len;
  return dv;
}

function send_buf() {
  if (bufs.length) {
    Bluetooth.write(btoa(bufs[0]));
  }
  Bluetooth.write('\n');
}

function remove_buf() {
  bufs.shift();
}

function on_accel(a) {
  var v = get_dv(7);
  v.setUint8(0, ACC);
  v.setInt16(1, a.x * 8192);
  v.setInt16(3, a.y * 8192);
  v.setInt16(5, a.z * 8192);
}

function on_mag(m) {
  var v = get_dv(7);
  v.setUint8(0, MAG);
  v.setInt16(1, m.x);
  v.setInt16(3, m.y);
  v.setInt16(5, m.z);
}

function on_gps(g) {
  if (g.fix == 0) return;
  var v = get_dv(26);
  v.setUint8(0, GPS);
  v.setInt32(1, g.lat * 11930464);
  v.setInt32(5, g.lon * 11930464);
  v.setUint16(9, clamp(g.alt * 16, 0, 65535));
  v.setFloat64(11, g.time.getTime());
  v.setUint8(19, g.fix);
  v.setUint8(20, clamp(g.hdop * 12, 0, 255));
  v.setUint8(21, g.satellites);
  v.setUint16(22, g.course * 182);
  v.setUint16(24, clamp(g.speed * 327, 0, 65535));
}

var clamp = (a, mi, ma) => a < mi ? mi : (ma < a ? ma : a);

function log(s) {
  Terminal.println(s);
}

g.clear();
Bangle.loadWidgets();
Bangle.drawWidgets();

log('# Cyclometer');
log('press top button to start');
Bangle.setGPSPower(true, 'cyc');

var satc = 0;
function ready(g) {
  if (g.fix) {
    Bangle.removeListener('GPS', ready);
    Bangle.buzz(500);
    log('GPS ready');
  } else if (g.satellites != satc) {
    satc = g.satellites;
    log('GPS satellites: ' + satc);
  }
}
Bangle.on('GPS', ready);

setWatch(() => {
  log('starting ...');
  Bangle.setLCDTimeout(0);
  Bangle.setOptions({btnLoadTimeout: 0});
  Bangle.setCompassPower(true, 'cyc');
  Bangle.on('accel', on_accel);
  Bangle.on('mag', on_mag);
  Bangle.on('GPS', on_gps);

  var tim_id = setInterval(() => {
    var v = get_dv(9);
    v.setUint8(0, TIM);
    v.setFloat64(1, getTime());
  }, 60 * 1000);

  var log_id = setInterval(() => {
    var m = process.memory();
    var p = Math.floor((m.usage / m.total) * 100);
    log('queue: ' + bufs.length + ' memory: ' + p + '%');
    if (67 <= p) {
      Bangle.buzz(500);
      setTimeout(() => Bangle.buzz(500), 1000);
    }
  }, 5 * 1000);

  log('started');
  log('hold top button for 3 seconds to stop');

  var cnt;
  var cnt_id;
  var btn_id = setWatch((e) => {
    if (e.state) {
      log('stop in 3');
      cnt = 3;
      cnt_id = setTimeout(stop, 1000);
      Bangle.buzz(300);
    } else if (cnt_id) {
      clearTimeout(cnt_id);
      cnt_id = undefined;
    }
  }, BTN1, {repeat: true, edge: 'both'});

  function stop() {
    cnt--;
    if (cnt == 0) {
      log('stopping ...');
      Bangle.setLCDTimeout(10);
      Bangle.setOptions({btnLoadTimeout: 1500});
      Bangle.setGPSPower(false, 'cyc');
      Bangle.setCompassPower(false, 'cyc');
      var _ = Bangle.removeListener.bind(Bangle);
      _('accel', on_accel);
      _('mag', on_mag);
      _('GPS', on_gps);
      clearInterval(tim_id);
      clearInterval(log_id);
      clearWatch(btn_id);
      log('stopped');
    } else {
      log('stop in ' + cnt);
      cnt_id = setTimeout(stop, 1000);
      Bangle.buzz(300);
    }
  }
}, BTN1);