Reponse header disordered after request sometimes

[flyinmind]

Following codes, run many times, the response header disordered.

        public void onRequest(AsyncHttpServerRequest req, final AsyncHttpServerResponse resp) {

...
pool.execute(new Runnable() {
@OverRide
public void run() {
....
resp.send(fm.contentType(), fm.read());
resp.end();
}
});
}

Expected is:
// { "framework": "Vue"}

// (function(modules) { // webpackBootstrap
// // The module cache
/******/ var installedModules = {};

Exactly response is:(Header is in body, and lost some content of the file)

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 24589
Content-Type: application/javascript; charset=utf-8

bb94-450a7ea35ac1
Host: 127.0.0.1:8080
Accept-Encoding: gzip, deflate, br
Connection: keep-alive

__(moduleId) {
//
// // Check if module is in cache
/******/ if(installedModules[moduleId]) {