diff --git a/source/event_hub.ts b/source/event_hub.ts
index 2eb0e446..6dfa92c7 100644
--- a/source/event_hub.ts
+++ b/source/event_hub.ts
@@ -182,6 +182,14 @@ export class EventHub {
     this._socketIo = io.connect(this._serverUrl, this._apiUser, this._apiKey);
     this._socketIo.on("connect", this._onSocketConnected);
     this._socketIo.on("ftrack.event", this._handle);
+    // SimpleSocketIOClient.connect is a singleton keyed on credentials, so
+    // a second EventHub built with the same credentials reuses an
+    // already-open socket. In that case the "connect" event has already
+    // fired and the listener above will never run on its own — run the
+    // handler now so this hub registers its reply subscription.
+    if (this._socketIo.socket.connected) {
+      this._onSocketConnected();
+    }
   }
 
   /**
diff --git a/test/event_hub.test.ts b/test/event_hub.test.ts
index 9be97f6b..9653c6dc 100644
--- a/test/event_hub.test.ts
+++ b/test/event_hub.test.ts
@@ -1,5 +1,6 @@
 import { EventHub } from "../source/event_hub.js";
 import { Event } from "../source/event.js";
+import SimpleSocketIOClient from "../source/simple_socketio.js";
 import { vi, describe, expect, beforeEach, afterEach, test } from "vitest";
 
 describe("EventHub", () => {
@@ -248,6 +249,222 @@ describe("EventHub", () => {
   });
 });
 
+describe("EventHub sharing a SimpleSocketIOClient singleton", () => {
+  // Regression test for the publishAndWaitForReply drop-on-second-Session
+  // bug: SimpleSocketIOClient.connect() is a singleton keyed on
+  // (serverUrl, apiUser, apiKey). A second EventHub built with the same
+  // credentials reuses the already-open socket. Each EventHub generates
+  // its own _id and registers its reply subscription inside
+  // _onSocketConnected, wired via socketIo.on("connect", ...). Because
+  // the "connect" event has already fired by the time the second hub
+  // attaches its listener, the listener would never run without the
+  // already-connected check in EventHub#connect — so the second hub
+  // would never tell the server about a subscription with its own _id,
+  // and replies targeted at it would be silently dropped on the server.
+  function makeSharedSocket() {
+    const handlers: Record<string, Array<(data: unknown) => void>> = {};
+    return {
+      socket: { connected: false },
+      emit: vi.fn(),
+      reconnect: vi.fn(),
+      disconnect: vi.fn(),
+      on(name: string, cb: (data: unknown) => void) {
+        (handlers[name] ||= []).push(cb);
+      },
+      fire(name: string, data: unknown) {
+        handlers[name]?.forEach((cb) => cb(data));
+      },
+    };
+  }
+
+  function emittedReplySubscriberIds(
+    socket: ReturnType<typeof makeSharedSocket>,
+  ) {
+    return socket.emit.mock.calls
+      .filter(
+        ([eventName, payload]) =>
+          eventName === "ftrack.event" &&
+          (payload as any)?.topic === "ftrack.meta.subscribe" &&
+          (payload as any)?.data?.subscription === "topic=ftrack.meta.reply",
+      )
+      .map(([, payload]) => (payload as any)?.data?.subscriber?.id);
+  }
+
+  test("second hub registers its reply subscription even when the shared socket is already connected", async () => {
+    const sharedSocket = makeSharedSocket();
+    // Stand in for SimpleSocketIOClient.connect's credential-keyed
+    // singleton: both EventHubs get the same socket object back.
+    const connectSpy = vi
+      .spyOn(SimpleSocketIOClient, "connect")
+      .mockReturnValue(sharedSocket as unknown as SimpleSocketIOClient);
+
+    try {
+      const hubA = new EventHub("http://ftrack.test", "user", "key") as any;
+      const hubB = new EventHub("http://ftrack.test", "user", "key") as any;
+
+      // Hub A connects before the socket opens (normal first-Session
+      // case). Its on("connect", ...) listener registers, then the
+      // socket finishes opening and fires "connect".
+      hubA.connect();
+      sharedSocket.socket.connected = true;
+      sharedSocket.fire("connect", {});
+      // publish() chains emits through a microtask; flush it.
+      await Promise.resolve();
+      await Promise.resolve();
+
+      const hubAReplySub = hubA._subscribers.find(
+        (s: any) => s.subscription === "topic=ftrack.meta.reply",
+      );
+      expect(hubAReplySub?.metadata.id).toBe(hubA._id);
+      expect(emittedReplySubscriberIds(sharedSocket)).toContain(hubA._id);
+
+      // Hub B connects AFTER the only "connect" event has fired. Without
+      // the already-connected fast-path in EventHub#connect, Hub B's
+      // _onSocketConnected would never run.
+      hubB.connect();
+      await Promise.resolve();
+      await Promise.resolve();
+
+      // With the fix in place, Hub B has its reply subscription
+      // registered locally and the server has been notified with Hub B's
+      // own _id — so future replies with target="id=<hubB._id>" will
+      // match a subscription on the server and reach this hub.
+      const hubBReplySub = hubB._subscribers.find(
+        (s: any) => s.subscription === "topic=ftrack.meta.reply",
+      );
+      expect(hubBReplySub?.metadata.id).toBe(hubB._id);
+      expect(emittedReplySubscriberIds(sharedSocket)).toContain(hubB._id);
+    } finally {
+      connectSpy.mockRestore();
+    }
+  });
+
+  test("publishAndWaitForReply routes replies to the correct hub on a shared socket", async () => {
+    const sharedSocket = makeSharedSocket();
+    const connectSpy = vi
+      .spyOn(SimpleSocketIOClient, "connect")
+      .mockReturnValue(sharedSocket as unknown as SimpleSocketIOClient);
+
+    try {
+      const hubA = new EventHub("http://ftrack.test", "user", "key") as any;
+      const hubB = new EventHub("http://ftrack.test", "user", "key") as any;
+
+      hubA.connect();
+      sharedSocket.socket.connected = true;
+      sharedSocket.fire("connect", {});
+      hubB.connect();
+      await Promise.resolve();
+      await Promise.resolve();
+
+      sharedSocket.emit.mockClear();
+
+      // Each hub kicks off a publishAndWaitForReply. They share one
+      // underlying socket — replies need to land on the correct hub.
+      const replyAPromise = hubA.publishAndWaitForReply(
+        new Event("foo.bar", { who: "A" }),
+      );
+      const replyBPromise = hubB.publishAndWaitForReply(
+        new Event("foo.bar", { who: "B" }),
+      );
+      await Promise.resolve();
+      await Promise.resolve();
+
+      // Pull the emitted ftrack.event payloads to learn each hub's
+      // event id and confirm source.id reflects the publishing hub.
+      const emittedFooBar = sharedSocket.emit.mock.calls
+        .filter(
+          ([eventName, payload]) =>
+            eventName === "ftrack.event" &&
+            (payload as any)?.topic === "foo.bar",
+        )
+        .map(([, payload]) => payload as any);
+      const eventA = emittedFooBar.find((p) => p.data.who === "A");
+      const eventB = emittedFooBar.find((p) => p.data.who === "B");
+      expect(eventA?.source?.id).toBe(hubA._id);
+      expect(eventB?.source?.id).toBe(hubB._id);
+
+      // Simulate the event server delivering a reply addressed to hub A.
+      // Both hubs receive every "ftrack.event" through the shared
+      // socket's handler chain — only the hub whose _replyCallbacks
+      // contains the matching inReplyToEvent should resolve.
+      sharedSocket.fire("ftrack.event", {
+        topic: "ftrack.meta.reply",
+        data: { result: "A-reply" },
+        source: { id: "responder" },
+        id: "server-reply-1",
+        inReplyToEvent: eventA.id,
+        target: `id=${hubA._id}`,
+      });
+      // …and a reply for hub B.
+      sharedSocket.fire("ftrack.event", {
+        topic: "ftrack.meta.reply",
+        data: { result: "B-reply" },
+        source: { id: "responder" },
+        id: "server-reply-2",
+        inReplyToEvent: eventB.id,
+        target: `id=${hubB._id}`,
+      });
+
+      const [replyA, replyB] = await Promise.all([
+        replyAPromise,
+        replyBPromise,
+      ]);
+      expect((replyA as any).data.result).toBe("A-reply");
+      expect((replyB as any).data.result).toBe("B-reply");
+    } finally {
+      connectSpy.mockRestore();
+    }
+  });
+
+  test("reconnect re-runs _onSocketConnected for both hubs without duplicating local subscribers", async () => {
+    const sharedSocket = makeSharedSocket();
+    const connectSpy = vi
+      .spyOn(SimpleSocketIOClient, "connect")
+      .mockReturnValue(sharedSocket as unknown as SimpleSocketIOClient);
+
+    try {
+      const hubA = new EventHub("http://ftrack.test", "user", "key") as any;
+      const hubB = new EventHub("http://ftrack.test", "user", "key") as any;
+
+      hubA.connect();
+      sharedSocket.socket.connected = true;
+      sharedSocket.fire("connect", {});
+      hubB.connect();
+      await Promise.resolve();
+      await Promise.resolve();
+
+      const replySubs = (hub: any) =>
+        hub._subscribers.filter(
+          (s: any) => s.subscription === "topic=ftrack.meta.reply",
+        );
+      expect(replySubs(hubA)).toHaveLength(1);
+      expect(replySubs(hubB)).toHaveLength(1);
+
+      // Simulate a reconnect: real handleOpen() fires "connect" again
+      // after the socket recovers. Both hubs are now wired up for it.
+      sharedSocket.emit.mockClear();
+      sharedSocket.fire("connect", {});
+      await Promise.resolve();
+      await Promise.resolve();
+
+      // _onSocketConnected catches NotUniqueError from the duplicate
+      // subscribe() call, so the local subscriber list stays at one
+      // entry per hub.
+      expect(replySubs(hubA)).toHaveLength(1);
+      expect(replySubs(hubB)).toHaveLength(1);
+
+      // …but both hubs do re-notify the server (via the for-loop in
+      // _onSocketConnected), which is the intended behaviour for
+      // surviving an event-server-side state loss.
+      const reNotifiedIds = emittedReplySubscriberIds(sharedSocket);
+      expect(reNotifiedIds).toContain(hubA._id);
+      expect(reNotifiedIds).toContain(hubB._id);
+    } finally {
+      connectSpy.mockRestore();
+    }
+  });
+});
+
 test("EventHub constructor", async () => {
   // Scenario 1
   const eventHub1 = new EventHub("https://ftrack.test", "testUser", "testKey", {