NFC stops working after a few minutes?

Basically a combination of the two, I use the following code:

var isLightOn = false;

NRF.nfcURL("https://www.google.com");
NRF.on('NFCon', function() { LED1.write(true);});
NRF.on('NFCoff', function() { LED1.write(false);});

setWatch(function() {
  isLightOn = !isLightOn;
  
  LED2.write(isLightOn);
}, BTN, { 
  repeat:true, 
  edge:"rising", 
  debounce:50 
});

And when I first hard reset the device it works on my Nexus 6P. If I wait, say, 15 minutes and try again, it no longer works (although the button press does.)