diff --git a/packages/javascript-api/src/lib/services/graphql/__tests__/graphql-subscriptions.spec.ts b/packages/javascript-api/src/lib/services/graphql/__tests__/graphql-subscriptions.spec.ts
index 51c0a92f..88ed8840 100644
--- a/packages/javascript-api/src/lib/services/graphql/__tests__/graphql-subscriptions.spec.ts
+++ b/packages/javascript-api/src/lib/services/graphql/__tests__/graphql-subscriptions.spec.ts
@@ -376,6 +376,79 @@ describe('GraphQL subscriptions', () => {
     subscription.unsubscribe();
   });
 
+  describe('WebSocket readyState guards', () => {
+    it('triggers reconnection when socket is not in OPEN state during sendMessage', async () => {
+      const service = fixture.graphqlService as any;
+      const handleDropSpy = jest.spyOn(service, 'handleConnectionDrop');
+
+      const sub = fixture.triggerSubscription();
+      await fixture.handleConnectionInit();
+      await fixture.consumeSubscribeMessage();
+
+      // mock-socket doesn't support simulating a half-closed socket,
+      // so we override readyState directly to test the guard
+      Object.defineProperty(service.socket, 'readyState', {
+        value: 0,
+        writable: true,
+      });
+      service.connectionStatus = ConnectionStatus.CONNECTED;
+
+      service.sendMessage('99', 'start', { query: 'subscription { test }' });
+
+      expect(handleDropSpy).toHaveBeenCalled();
+      expect(fixture.server.messagesToConsume.pendingItems).toHaveLength(0);
+
+      sub.unsubscribe();
+    });
+
+    it('sendPing skips sending when socket is not OPEN but still sets pong timeout', () => {
+      const service = fixture.graphqlService as any;
+      service.socket = { readyState: 0, send: jest.fn() };
+      service.pongTimeout = null;
+
+      service.sendPing();
+
+      expect(service.pongTimeout).not.toBeNull();
+      expect(service.socket.send).not.toHaveBeenCalled();
+
+      clearTimeout(service.pongTimeout);
+    });
+
+    it('triggers reconnection when re-subscription fails during connection_ack', async () => {
+      const service = fixture.graphqlService as any;
+      const handleDropSpy = jest.spyOn(service, 'handleConnectionDrop');
+      const loggerWarnSpy = jest.spyOn(service.logger, 'warn');
+
+      const sub1 = fixture.triggerSubscription('subscription { first }');
+      await fixture.handleConnectionInit();
+      await fixture.consumeSubscribeMessage('subscription { first }');
+
+      await fixture.closeWithCode(1001);
+      fixture.openServer();
+      await fixture.waitForConnection();
+      await fixture.consumeInitMessage();
+
+      // mock-socket doesn't support simulating a half-closed socket,
+      // so we override readyState directly to test the guard
+      Object.defineProperty(service.socket, 'readyState', {
+        value: 0,
+        writable: true,
+      });
+      fixture.sendMessageToClient({ type: 'connection_ack' });
+
+      // Allow mock-socket message delivery to settle
+      await new Promise((r) => setTimeout(r, 10));
+
+      const resubWarnings = loggerWarnSpy.mock.calls.filter((call) =>
+        String(call[0]).includes('Failed to re-subscribe'),
+      );
+      expect(resubWarnings).toHaveLength(1);
+      expect(handleDropSpy).toHaveBeenCalled();
+
+      sub1.unsubscribe();
+    });
+  });
+
   function useFakeSetInterval() {
     jest.useFakeTimers({
       doNotFake: [
diff --git a/packages/javascript-api/src/lib/services/graphql/graphql.service.ts b/packages/javascript-api/src/lib/services/graphql/graphql.service.ts
index 62052145..87458fff 100644
--- a/packages/javascript-api/src/lib/services/graphql/graphql.service.ts
+++ b/packages/javascript-api/src/lib/services/graphql/graphql.service.ts
@@ -374,21 +374,32 @@ export class GraphqlService {
           case MessageType.GQL_CONNECTION_KEEP_ALIVE:
             break;
 
-          case MessageType.GQL_CONNECTION_ACK:
+          case MessageType.GQL_CONNECTION_ACK: {
             this.connectionAttemptsCount = 0;
             this.setConnectionStatus(ConnectionStatus.CONNECTED);
             this.logger.info('Connected to websocket');
             this.startConnectionMonitoring();
-            this.subscriptions.forEach((subscription) => {
+            let resubscriptionFailed = false;
+            for (const subscription of this.subscriptions) {
               const payload = { query: subscription.query };
               const msg = JSON.stringify({
                 id: subscription.id,
                 type: MessageType.GQL_START,
                 payload,
               });
-              this.sendRawMessage(msg);
-            });
+              if (!this.sendRawMessage(msg)) {
+                this.logger.warn(
+                  `Failed to re-subscribe ${this.subscriptions.length} subscription(s): WebSocket not open`,
+                );
+                resubscriptionFailed = true;
+                break;
+              }
+            }
+            if (resubscriptionFailed) {
+              this.handleConnectionDrop();
+            }
             break;
+          }
 
           case MessageType.GQL_DATA:
             this.subscriptionObserverMap[message.id]?.next(
@@ -439,14 +450,21 @@ export class GraphqlService {
 
   private sendMessage(id: string, type: MessageType, payload: any) {
     if (this.connectionStatus === ConnectionStatus.CONNECTED) {
-      this.sendRawMessage(JSON.stringify({ id, type, payload }));
+      if (!this.sendRawMessage(JSON.stringify({ id, type, payload }))) {
+        this.logger.warn('Message dropped: WebSocket is not in OPEN state');
+        this.handleConnectionDrop();
+      }
     } else {
       this.openSocket();
     }
   }
 
-  private sendRawMessage(message: any) {
-    this.socket.send(message);
+  private sendRawMessage(message: string): boolean {
+    if (this.socket?.readyState === WebSocket.OPEN) {
+      this.socket.send(message);
+      return true;
+    }
+    return false;
   }
 
   private generateOperationId(): string {
@@ -484,9 +502,7 @@ export class GraphqlService {
       this.handleConnectionDropWithThisBound,
       PONG_TIMEOUT_IN_MS,
     );
-    if (this.socket) {
-      this.sendRawMessage(JSON.stringify({ type: MessageType.GQL_PING }));
-    }
+    this.sendRawMessage(JSON.stringify({ type: MessageType.GQL_PING }));
   }
 
   private handleConnectionDrop(): void {