NRF.setScan() stops working

call this .... manually every 5 seconds or so, is that ok?

Yes, that should be totally fine.

The problem is that it can takes a long time (like 3-5 seconds) for scan to pick up the changes

Do you know roughly how often you're getting BLE advertisements from setScan? I think it's quite likely you're in a reasonably congested area and there are so many devices it's having trouble processing fast enough

Can NRF.requestDevice read advertising data (the state) from the other Puck?

Yes - you'll get the exact same response you would from setScan.

For instance if you do this it should be really nice and easy:

NRF.requestDevice({filters:[{name:"Pixl.js 8999"}]}).then(function(dev) {
  if (dev.manufacturerData)
    print("State is "+dev.manufacturerData[0]);
})

It's a shame you can't filter by id at the moment though - only name/services