Uncaught InternalError: BLE task completed that wasn't scheduled (3/4)

Thanks Gordon. Just tried latest Pixl.js build. The BLE error ended up being user error. If I don't use the full UUID for the characteristic then it should be 0x2A37 not "0x2A37".

So errors now gone but still no change notifications.

Note that a non-changing value can be read fine e.g. Body Sensor Position gives 1 (Chest) correctly with this:

return s.getCharacteristic(0x2a38);

Just looking at NRF Connect logs, it does gatt.setCharacteristicNotification(). Is that done under the hood in c.on('characteristicvaluechanged' ?

D 12:33:18.447 gatt.setCharacteristicNotification(00002a37-0000-1000-8000-00805f9b34fb, true)
D 12:33:18.448 gatt.writeDescriptor(00002902-0000-1000-8000-00805f9b34fb, value=0x0100)
I 12:33:18.514 Data written to descr. 00002902-0000-1000-8000-00805f9b34fb, value: (0x) 01-00
A 12:33:18.514 "Notifications enabled" sent
V 12:33:18.519 Notifications enabled for 00002a37-0000-1000-8000-00805f9b34fb
I 12:33:19.314 Connection parameters updated (interval: 1012.5ms, latency: 0, timeout: 10120ms)
I 12:33:21.340 Notification received from 00002a37-0000-1000-8000-00805f9b34fb, value: (0x) 00-47
A 12:33:21.340 "Heart Rate Measurement: 71 bpm,

I found some info that says HRMs specifically need to be told to send updates, so I added:

 return device.getPrimaryService(0x1801);
    }).then(function (s) {
        Terminal.println("Service ", s);
        return s.getCharacteristic(0x2a05);
    }).then(function (c) {
        return c.writeValue(0x0100);

But still no joy.