This looks to be broken by JDK-8179021.

It can be reproduced with a simple connect, communicate round trip with wss scheme. Please refer the test below. Keystore will be attached.
If comment out ssl context and use ws://xxx url, it works well.

import static java.lang.System.out;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.KeyStore;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ExecutionException;

import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManagerFactory;

import jdk.incubator.http.HttpClient;
import jdk.incubator.http.WebSocket;
import jdk.incubator.http.WebSocket.Listener;
import jdk.incubator.http.WebSocket.MessagePart;

public class WSSTest {

    private static final String ALGORITHM = "SunX509";
    private static final char[] PASSWORD = "changeit".toCharArray();

    public static void main(String[] args) throws URISyntaxException, InterruptedException, ExecutionException, IOException {
        Listener l = new Listener() {

            @Override
            public CompletionStage<?> onClose(WebSocket arg0, int arg1,
                    String arg2) {
                System.out.println("onClose");
                return Listener.super.onClose(arg0, arg1, arg2);
            }

            @Override
            public void onOpen(WebSocket arg0) {
                System.out.println("onOpen");
                Listener.super.onOpen(arg0);
            }

            @Override
            public CompletionStage<?> onText(WebSocket arg0, CharSequence text,
                    MessagePart arg2) {
                System.out.println("onText:" + text);
                return Listener.super.onText(arg0, text, arg2);
            }

            @Override
            public void onError(WebSocket webSocket, Throwable error) {
                System.err.println("onError");
                System.err.println(error);
            }
        };

        URI uri = new URI(
                "wss url"
                );
        WebSocket ws;
        HttpClient client = HttpClient.newBuilder()
                .sslContext(sslContext())
                .build();
        ws = client.newWebSocketBuilder(uri, l).buildAsync().get();

        out.println(" connected ");
        ws.sendText("Hello!", true);
        ws.sendClose(WebSocket.NORMAL_CLOSURE, "Normal Close").get();
        out.println(" closed");
        ws.abort();
    }

    /** Gets a SSLContext for secure connections. */
    public static SSLContext sslContext() {
        SSLContext sslContext = null;
        Path keyPath = Paths.get(".", "keystore.jks");
        try (InputStream keyStoreIn = new FileInputStream(
                keyPath.toFile())) {
            KeyStore keyStore = KeyStore.getInstance("JKS");
            keyStore.load(keyStoreIn, PASSWORD);

            KeyManagerFactory km = KeyManagerFactory.getInstance(ALGORITHM);
            km.init(keyStore, PASSWORD);

            TrustManagerFactory tm = TrustManagerFactory
                    .getInstance(ALGORITHM);
            tm.init(keyStore);

            sslContext = SSLContext.getInstance("TLS");
            sslContext.init(km.getKeyManagers(), tm.getTrustManagers(),
                    null);
            System.out.println("SSLContext initialized");
        } catch (Exception e) {
            System.err.println("Failed to get SSLContext");
            throw new RuntimeException(e);
        }
        return sslContext;
    }
}

Please refer to the jstack output attached. It seems websocket is stuck at onOpen
"HttpClient_worker" #14 daemon prio=5 os_prio=0 tid=0x0000000036d7c800 nid=0x1804 runnable [0x0000000037ece000]
   java.lang.Thread.State: RUNNABLE
at sun.nio.ch.SocketDispatcher.read0(java.base@9-ea/Native Method)
at sun.nio.ch.SocketDispatcher.read(java.base@9-ea/SocketDispatcher.java:43)
at sun.nio.ch.IOUtil.readIntoNativeBuffer(java.base@9-ea/IOUtil.java:223)
at sun.nio.ch.IOUtil.read(java.base@9-ea/IOUtil.java:197)
at sun.nio.ch.SocketChannelImpl.read(java.base@9-ea/SocketChannelImpl.java:382)
- locked <0x00000006d1365a38> (a java.lang.Object)
at jdk.incubator.http.SSLDelegate$EngineWrapper.recvAndUnwrap(jdk.incubator.httpclient@9-ea/SSLDelegate.java:280)
- locked <0x00000006d136fa00> (a java.lang.Object)
at jdk.incubator.http.SSLDelegate.recvData(jdk.incubator.httpclient@9-ea/SSLDelegate.java:362)
at jdk.incubator.http.SSLConnection.readImpl(jdk.incubator.httpclient@9-ea/SSLConnection.java:179)
at jdk.incubator.http.SSLConnection.readImpl(jdk.incubator.httpclient@9-ea/SSLConnection.java:166)
at jdk.incubator.http.HttpConnection.read(jdk.incubator.httpclient@9-ea/HttpConnection.java:331)
at jdk.incubator.http.RawChannelImpl.read(jdk.incubator.httpclient@9-ea/RawChannelImpl.java:114)
at jdk.incubator.http.internal.websocket.Receiver.readData(jdk.incubator.httpclient@9-ea/Receiver.java:142)
at jdk.incubator.http.internal.websocket.Receiver.pushOnce(jdk.incubator.httpclient@9-ea/Receiver.java:126)
at jdk.incubator.http.internal.websocket.Receiver.pushContinuously(jdk.incubator.httpclient@9-ea/Receiver.java:121)
at jdk.incubator.http.internal.websocket.Receiver$$Lambda$71/663162477.run(jdk.incubator.httpclient@9-ea/Unknown Source)
at jdk.incubator.http.internal.websocket.CooperativeHandler.lambda$asyncOf$0(jdk.incubator.httpclient@9-ea/CooperativeHandler.java:204)
at jdk.incubator.http.internal.websocket.CooperativeHandler$$Lambda$72/1892324013.accept(jdk.incubator.httpclient@9-ea/Unknown Source)
at jdk.incubator.http.internal.websocket.CooperativeHandler.handle(jdk.incubator.httpclient@9-ea/CooperativeHandler.java:144)
at jdk.incubator.http.internal.websocket.Receiver.request(jdk.incubator.httpclient@9-ea/Receiver.java:101)
at jdk.incubator.http.internal.websocket.WebSocketImpl.request(jdk.incubator.httpclient@9-ea/WebSocketImpl.java:363)
at jdk.incubator.http.WebSocket$Listener.onOpen(jdk.incubator.httpclient@9-ea/WebSocket.java:307)
at jdk.incubator.http.internal.websocket.WebSocketImpl.signalOpen(jdk.incubator.httpclient@9-ea/WebSocketImpl.java:162)
- locked <0x00000006d0c9edb8> (a java.lang.Object)
at jdk.incubator.http.internal.websocket.WebSocketImpl.lambda$newInstanceAsync$0(jdk.incubator.httpclient@9-ea/WebSocketImpl.java:116)
at jdk.incubator.http.internal.websocket.WebSocketImpl$$Lambda$28/682376643.apply(jdk.incubator.httpclient@9-ea/Unknown Source)
at java.util.concurrent.CompletableFuture$UniApply.tryFire(java.base@9-ea/CompletableFuture.java:642)
at java.util.concurrent.CompletableFuture.postComplete(java.base@9-ea/CompletableFuture.java:506)
at java.util.concurrent.CompletableFuture.complete(java.base@9-ea/CompletableFuture.java:2073)
at jdk.incubator.http.ResponseProcessors$NullProcessor.onComplete(jdk.incubator.httpclient@9-ea/ResponseProcessors.java:336)
at jdk.incubator.http.BlockingPushPublisher.acceptData(jdk.incubator.httpclient@9-ea/BlockingPushPublisher.java:65)
at jdk.incubator.http.AbstractPushPublisher.consume(jdk.incubator.httpclient@9-ea/AbstractPushPublisher.java:51)
at jdk.incubator.http.AbstractPushPublisher$$Lambda$67/1278626421.accept(jdk.incubator.httpclient@9-ea/Unknown Source)
at jdk.incubator.http.ResponseContent.pushBodyFixed(jdk.incubator.httpclient@9-ea/ResponseContent.java:290)
at jdk.incubator.http.ResponseContent.pushBody(jdk.incubator.httpclient@9-ea/ResponseContent.java:112)
at jdk.incubator.http.Http1Response.lambda$readBody$2(jdk.incubator.httpclient@9-ea/Http1Response.java:157)
at jdk.incubator.http.Http1Response$$Lambda$65/808773358.run(jdk.incubator.httpclient@9-ea/Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@9-ea/ThreadPoolExecutor.java:1161)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@9-ea/ThreadPoolExecutor.java:635)
at java.lang.Thread.run(java.base@9-ea/Thread.java:844)