NFC stops working after a few minutes?

OK, it's really a bit weird. Things first started working again, but then again did not. I've now written some small interval that changes the URL every 5 seconds, I was able to get the first url transferred to my mobile via NFC, but then nothing else worked. But I still see the log outputs in the espruine web console.

var url = "https://api.yaas.io/bullseye/"; 
var counter = 0; 
setInterval(function() { NRF.nfcURL(url + counter++);   console.log(url + counter); }, 5000);