NRC received events ( NRF.on('NFCrx') )

I'm using Puck.js (Espruino v2.01) and I want to be able to manipulate variables based on data that is written to the NFC tag using NFCrx.
If I use the 'NFCon' event, and console log based on that, everything works when I scan NFC:

>NRF.on('NFCon', () => { console.log("test"); });
=undefined
test
test
test

But when I use the NFCrx event instead, after NFCStart of course, the event callback is not called (almost as if the event is not registered):

>NRF.nfcStart();
=new Uint8Array([95, 193, 71, 81, 42, 138, 1, 165, 4, 3]).buffer
>NRF.on('NFCrx', (rx) => { console.log(rx); });
=undefined
>NRF.on('NFCrx', (rx) => { NRF.nfcSend("test"); });
=undefined
>NRF.on('NFCrx', (rx) => { console.log("test"); });
=undefined

What am I missing?
Thanks in advance