I looked into it more. But it seems websocket library depended by android device sdk has some TLS connection issue.
See more detail here. It could be related.
Another possible solution is not to use TLS connection for WebSocket. It is not desirable but good enough for prototyping in your case.
To do that, you can change
static final String MODEWEBSOCKETURL = "wss://api.tinkermode.com:443/devices/";
static final String MODEWEBSOCKETURL = "ws://api.tinkermode.com/devices/";