title: Webflux parallel connections somehow limited to 256
body: <p>I have a simple setup of server and client:</p>
  
  <pre><code>Flux.range(1, 5000)
          .subscribeOn(Schedulers.parallel())
          .flatMap(i -&gt; WebClient.create()
              .method(HttpMethod.POST)
              .uri("http://localhost:8080/test")
              .body(Mono.just(String.valueOf(i)), String.class)
              .exchange())
          .publishOn(Schedulers.parallel())
          .subscribe(response -&gt;
              response.bodyToMono(String.class)
                  .publishOn(Schedulers.elastic())
                  .subscribe(body -&gt; log.info("{}", body)));
  </code></pre>
  
  <p>here is the client:</p>
  
  <pre><code>@PostMapping
  public Mono&lt;String&gt; test(@RequestBody Mono&lt;String&gt; body) {
      return body.delayElement(Duration.ofSeconds(5));
  }
  </code></pre>
  
  <p>Both things run on netty. Maybe someone has an idea what is causing this behavior?</p>