Transport close when using 2.1.1 client concurrent sending data to 2.0.9 netty-socketio

[solus-li]

I'm using Java.
The java client is socket.io-client:2.1.1;
The java server is netty-socketio:2.0.9;
When I create a thread pool using Executors.newCachedThreadPool() to send data. Each thread sends data in batches, with the batch size set to 1M. When the concurrent data volume over 20M, the connection disconnects and I get a 'transport close' status code.
And there is no additional error information to help diagnose why the client closed.