NRF.setServices .. onWrite called twice

I'm not sure what to suggest here I'm afraid... The way setServices works it shouldn't really be able to call the handler twice. What if you add some kind of 'print' statement inside onWrite: (e) => cc.read(new Uint8Array(e.data)) just in case your cc.read method is doing something internally?

You could also check on your watch to ensure your code isn't in there twice (eg in two separate files). You could check with:

require("Storage").list().forEach(f=>{
  if (require("Storage").read(f).includes("0xf012")) print(f);
});

If it's ok, it should be in just .boot0 and in your app.boot.js file