Vert.x httpclient - 3.5.0 throws exception "Connection was closed" intermittently

I have vert.x app which is consuming api REST over json but intermittently I am seeing exception with reason "Connection was closed". Below are my details -

1. please share your inputs if anything wrong in the configuration. may be creating scheduler or instantiating httpclient ?
2. on a different note is it advisable to use same http client to call more than 1 different api's on the same host and port ?

Vert.x Version: 3.5.0

import io.vertx.core.http.HttpClient;

private static Scheduler scheduler = 
Schedulers.from(Executors.newFixedThreadPool(8));

// http client instantiated at the time of verticle startup
HttpClient httpclient = vertx.createHttpClient(getHttpClientOptions());

public static HttpClientOptions getHttpClientOptions() {
    return new HttpClientOptions()  
            .setKeepAlive(true)
            .setMaxPoolSize(100)
            .setPipelining(true)
            .setDefaultHost(xxxx.xxxx.com)
            .setDefaultPort(8084)
            .setSsl(true);
}

 // invoke api call
public static Single<Response> invokePOSTServiceAsync(String  reqBodyStr, String endpointURI) throws Exception {
        try{
        return Single.create((SingleEmitter<Response> emitter) -> {
            HttpClientRequest request = httpClient.post(endpointURI);
      request.putHeader("Content-type","application/json")  
            request.exceptionHandler(error -> {
                        LOG.error("ExceptionHandler "+error.getMessage());
                        emitter.onError(new Throwable(" Failure"));
                    })
                    .handler(response -> {
                        int statusCode = response.statusCode();
                        if (statusCode == 200) {
                            response.bodyHandler(body -> {
                                StringBuilder responseData = new StringBuilder();
                                responseData.append(body);
                                emitter.onSuccess(new Response(statusCode,responseData.toString(),"","",null));
                            });
                        } else {
                            emitter.onError(new Throwable(" Failure"));
                        }
                    })
                    .putHeader(HttpHeaders.CONTENT_LENGTH, reqBodyStr.length() + "")
                    .setTimeout(6000)
                    .write(reqBodyStr)
                    .end();
                }).subscribeOn(scheduler); 
        }catch(Exception exe){
            exe.printStackTrace();
            return null;
        }
    }