Puck to Puck Communication - Some Errors

I tweaked some puck example code from various places to make a remote button for a puck. A silly use case but a chance to try out connecting to a puck. This is the target device. A button press turns the blinking on and off and changes the color.

var on = false;
var stop = 0;
var c = 1;
function startBlink() {
  on = false;
  if (stop !== 0) {
    clearInterval(stop); stop = 0;
    LED1.write(0); LED2.write(0); LED3.write(0);
  }
  else {
    switch (c) {
      case 1:
        led = LED1; //print("red");
        c = 2;
        break;
      case 2:
        led = LED2; //print("green");
        c = 3;
        break;
      case 3:
        led = LED3; //print("blue");
        c = 1;
        break;
    }
    stop = setInterval(function() {
      on = !on;
      led.write(on);
    }, 500);
  }
}
setWatch(startBlink, BTN, { repeat:true, edge:'rising', debounce : 20 });

And this is the remote button code. It will try and connect to the target and issue a command that simulates pressing the button.

function flashLed(led) {
  flashLed.count = 0;
  flashLed.h = setInterval(function() {
    if (flashLed.count++ == 6) {
      led.write(0);
      clearInterval(flashLed.h);
      flashLed.count = 0;
    }
    else {
      led.write(flashLed.on = !flashLed.on);
    }
  }, 500);
}

function sendCmd() {
  var name = "Puck.js d958"; // change me to your target puck's name
  var gatt = null;
  console.log("searching for " + name);
  NRF.requestDevice(
    {
      filters: [
        { namePrefix: name }
        //{ namePrefix: 'EspruinoHub' }
      ]
    }
  ).then(function(dev) {
      console.log("device found", dev);
      return dev.gatt.connect();
    }
  ).then(function(conn) {
      gatt = conn;
      console.log("connected", conn);
      return conn.getPrimaryService("6e400001-b5a3-f393-e0a9-e50e24dcca9e");
    }
  ).then(function(s) {
      console.log("service found", s);
      return s.getCharacteristic("6e400002-b5a3-f393-e0a9-e50e24dcca9e");
    }
  ).then(function(c) {
      console.log("characteristic found", c);
      c.writeValue("startBlink()\n");
    }
  ).then(function() {
      gatt.disconnect();
      console.log("disconnected");
    }
  ).then(function() {
      console.log("success!");
      flashLed(LED2);
    }
  ).catch(function(e) {
      console.log( "catch caught an error!");
      console.log( "error:", e );
      if (gatt !== null) {
        gatt.disconnect();
        console.log("disconnected");
      }
      flashLed(LED1);
      console.log("all done");
    }
  ).catch(function(e) {
      console.log( "catch caught another error!");
      console.log( "error:", e );
      flashLed(LED1);
      console.log("all done");
    }
  );
}
setWatch(sendCmd, "D0", { repeat:true, edge:'rising', debounce : 50 });

It works about half the time. But very often I get the following error output. I have tried to look up the BLE error code but I can't find anything on it.

searching for Puck.js d958
device found BluetoothDevice {
  "id": "ca:78:ab:df:d9:58 random",
  "rssi": -57,
  "services": [  ],
  "data": new ArrayBuffer([2, 1, 5, 13, 9, 80, 117, 99, 107, 46, 106, 115, 32, 100, 57, 53, 56]),
  "name": "Puck.js d958"
 }
connected BluetoothRemoteGATTServer {
  "device": BluetoothDevice {
    "id": "ca:78:ab:df:d9:58 random",
    "rssi": -57,
    "services": [  ],
    "data": new ArrayBuffer([2, 1, 5, 13, 9, 80, 117, 99, 107, 46, 106, 115, 32, 100, 57, 53, 56]),
    "name": "Puck.js d958",
    "gatt":  ...
   },
  "connected": true }
catch caught an error!
error: Error {
  "msg": "Got BLE error code 12290",
  "type": "Error",
  "stack": " at line 35 col 75\n...5a3-f393-e0a9-e50e24dcca9e\");\n                              ^\nin function called from system\n"
 }
catch caught another error!
error: Error {
  "msg": "Got BLE error code 8",
  "type": "Error",
  "stack": " at line 57 col 25\n        gatt.disconnect();\n                        ^\nin function called from system\n"
 }
all done
> 

This is the interesting bit:

error: Error {
"msg": "Got BLE error code 12290",
"type": "Error",
"stack": " at line 35 col 75\n...5a3-f393-e0a9-e50e24dcca9e\");\n ^\nin function called from system\n"

The puck appears to connect ok but then it looks like the code blows up attempting to get the service. Like I said this happens about half the time. When it works properly it works very well.

Clearly I am not doing something entirely right here. Any thoughts would be appreciated.