socket.io-client: Invalid namespace error (only on Linux Ubuntu)

I have a NodeJS script meant to run on a device, and an app on a server. I want to connect the device to the /device namespace on the server. This works perfectly on Windows. On Ubuntu however the device just never connects. Passing a DEBUG env variable in gives this output:

socket.io-client:url parse http://localhost:3000/device +0ms
  socket.io-client new io instance for http://localhost:3000/device +7ms
  socket.io-client:manager readyState closed +5ms
  socket.io-client:manager opening http://localhost:3000/device +0ms
  engine.io-client:socket creating transport "websocket" +3ms
  engine.io-client:socket setting transport websocket +47ms
  socket.io-client:manager connect attempt will timeout after 20000 +2ms
  socket.io-client:manager readyState opening +4ms
  engine.io-client:socket socket receive: type "open", data "{"sid":"oYxMG7iQuy2Rp7LWAAAN","upgrades":[],"pingInterval":25000,"pingTimeout":60000}" +51ms
  engine.io-client:socket socket open +1ms
  socket.io-client:manager open +1ms
  socket.io-client:manager cleanup +1ms
  socket.io-client:socket transport is open - connecting +1ms
  socket.io-client:manager writing packet {"type":0,"query":"deviceId=123456789abcdef","nsp":"/device"} +1ms
  socket.io-parser encoding packet {"type":0,"query":"deviceId=123456789abcdef","nsp":"/device?deviceId=123456789abcdef"} +0ms
  socket.io-parser encoded {"type":0,"query":"deviceId=123456789abcdef","nsp":"/device?deviceId=123456789abcdef"} as 0/device?deviceId=123456789abcdef +1ms
  engine.io-client:socket flushing 1 packets in socket +1ms
  engine.io-client:socket socket receive: type "message", data "0" +14ms
  socket.io-parser decoded 0 as {"type":0,"nsp":"/"} +2ms
  engine.io-client:socket socket receive: type "message", data "4/device?deviceId=123456789abcdef,"Invalid namespace"" +3ms
  socket.io-parser decoded 4/device?deviceId=123456789abcdef,"Invalid namespace" as {"type":4,"nsp":"/device?deviceId=123456789abcdef","data":"Invalid namespace"} +2ms

I.e. the namespace seems to be invalid. I have no idea why, as this code runs perfectly on Windows. My device (client) code:

const socket = io.connect('http://localhost:3000/device', {
    transports: ['websocket'],
    secure: true,
    query: { deviceId: '123456789abcdef' }
});

socket.on('connect', function() {
    console.log('Connection to server established');
})

My server code:

  const device = io.of('/device'),
      portal = io.of('/portal');

  device.on('connection', function(socket) {
      console.log('Connection made');
  })

Any ideas would be useful.