diff --git a/flow-server/src/main/java/com/vaadin/flow/server/communication/UidlRequestHandler.java b/flow-server/src/main/java/com/vaadin/flow/server/communication/UidlRequestHandler.java
index d7d2c1a76af..17b3a0f7c0e 100644
--- a/flow-server/src/main/java/com/vaadin/flow/server/communication/UidlRequestHandler.java
+++ b/flow-server/src/main/java/com/vaadin/flow/server/communication/UidlRequestHandler.java
@@ -20,6 +20,7 @@
 import java.io.OutputStream;
 import java.io.StringWriter;
 import java.io.Writer;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -66,15 +67,13 @@
 public class UidlRequestHandler extends SynchronizedRequestHandler
         implements SessionExpiredHandler {
 
+    private AtomicReference<ServerRpcHandler> rpcHandler = new AtomicReference<>();
 
-    private ServerRpcHandler rpcHandler;
-
-    public static final Pattern HASH_PATTERN = Pattern.compile("window.location.hash ?= ?'(.*?)'");
+    public static final Pattern HASH_PATTERN = Pattern
+            .compile("window.location.hash ?= ?'(.*?)'");
     public static final Pattern URL_PATTERN = Pattern.compile("^(.*)#(.+)$");
-    public static final String PUSH_STATE_HASH =
-            "setTimeout(() => history.pushState(null, null, location.pathname + location.search + '#%s'));";
-    public static final String PUSH_STATE_LOCATION =
-            "setTimeout(() => history.pushState(null, null, '%s'));";
+    public static final String PUSH_STATE_HASH = "setTimeout(() => history.pushState(null, null, location.pathname + location.search + '#%s'));";
+    public static final String PUSH_STATE_LOCATION = "setTimeout(() => history.pushState(null, null, '%s'));";
 
     private static final String SYNC_ID = '"' + SERVER_SYNC_ID + '"';
     private static final String RPC = RPC_INVOCATIONS;
@@ -141,8 +140,7 @@ private void writeRefresh(VaadinResponse response) throws IOException {
         commitJsonResponse(response, json);
     }
 
-    void writeUidl(UI ui, Writer writer, boolean resync)
-            throws IOException {
+    void writeUidl(UI ui, Writer writer, boolean resync) throws IOException {
         JsonObject uidl = createUidl(ui, resync);
 
         if (ui instanceof JavaScriptBootstrapUI) {
@@ -184,11 +182,12 @@ public boolean handleSessionExpired(VaadinRequest request,
     }
 
     private ServerRpcHandler getRpcHandler(VaadinSession session) {
-        session.checkHasLock();
-        if (rpcHandler == null) {
-            rpcHandler = createRpcHandler();
+        ServerRpcHandler handler = rpcHandler.get();
+        if (handler == null) {
+            rpcHandler.compareAndSet(null, createRpcHandler());
+            handler = rpcHandler.get();
         }
-        return rpcHandler;
+        return handler;
     }
 
     /**
@@ -330,4 +329,3 @@ private String removeHashInRpc(JsonArray rpc) {
         return null;
     }
 }
-