diff --git a/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Grpc/Services/ScadaGrpcService.cs b/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Grpc/Services/ScadaGrpcService.cs
index 63fdd61..0f961da 100644
--- a/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Grpc/Services/ScadaGrpcService.cs
+++ b/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Grpc/Services/ScadaGrpcService.cs
@@ -360,7 +360,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.Grpc.Services
                 throw new RpcException(new GrpcStatus(StatusCode.Unauthenticated, "Invalid session"));
             }
 
-            var reader = _subscriptionManager.Subscribe(
+            var reader = await _subscriptionManager.SubscribeAsync(
                 request.SessionId, request.Tags, context.CancellationToken);
 
             try
diff --git a/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Subscriptions/SubscriptionManager.cs b/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Subscriptions/SubscriptionManager.cs
index 739538c..05e709a 100644
--- a/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Subscriptions/SubscriptionManager.cs
+++ b/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Subscriptions/SubscriptionManager.cs
@@ -42,8 +42,10 @@ namespace ZB.MOM.WW.LmxProxy.Host.Subscriptions
 
         /// <summary>
         ///     Creates a subscription for a client. Returns a ChannelReader to stream from.
+        ///     Awaits COM subscription creation so the initial OnDataChange callback
+        ///     is not missed.
         /// </summary>
-        public ChannelReader<(string address, Vtq vtq)> Subscribe(
+        public async Task<ChannelReader<(string address, Vtq vtq)>> SubscribeAsync(
             string clientId, IEnumerable<string> addresses, CancellationToken ct)
         {
             var channel = Channel.CreateBounded<(string address, Vtq vtq)>(
@@ -83,10 +85,13 @@ namespace ZB.MOM.WW.LmxProxy.Host.Subscriptions
                 _rwLock.ExitWriteLock();
             }
 
-            // Create MxAccess COM subscriptions for newly subscribed tags
+            // Create MxAccess COM subscriptions — awaited so the initial
+            // OnDataChange (first value delivery after AdviseSupervisory)
+            // is not lost. The channel and routing are already set up above,
+            // so any callback that fires during this call will be delivered.
             if (newTags.Count > 0)
             {
-                _ = CreateMxAccessSubscriptionsAsync(newTags);
+                await CreateMxAccessSubscriptionsAsync(newTags);
             }
 
             // Register cancellation cleanup
diff --git a/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Health/HealthCheckServiceTests.cs b/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Health/HealthCheckServiceTests.cs
index a735907..64b1827 100644
--- a/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Health/HealthCheckServiceTests.cs
+++ b/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Health/HealthCheckServiceTests.cs
@@ -104,7 +104,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Health
             for (int i = 0; i < 101; i++)
             {
                 using var cts = new CancellationTokenSource();
-                sm.Subscribe("client-" + i, new[] { "tag1" }, cts.Token);
+                await sm.SubscribeAsync("client-" + i, new[] { "tag1" }, cts.Token);
             }
 
             var svc = new HealthCheckService(client, sm, pm);
diff --git a/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Subscriptions/SubscriptionManagerTests.cs b/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Subscriptions/SubscriptionManagerTests.cs
index b12af80..cb60a1b 100644
--- a/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Subscriptions/SubscriptionManagerTests.cs
+++ b/lmxproxy/tests/ZB.MOM.WW.LmxProxy.Host.Tests/Subscriptions/SubscriptionManagerTests.cs
@@ -47,11 +47,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void Subscribe_ReturnsChannelReader()
+        public async Task Subscribe_ReturnsChannelReader()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Tag1", "Tag2" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Tag1", "Tag2" }, cts.Token);
             reader.Should().NotBeNull();
         }
 
@@ -60,7 +60,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
 
             var vtq = Vtq.Good(42.0);
             sm.OnTagValueChanged("Motor.Speed", vtq);
@@ -76,8 +76,8 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader1 = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
-            var reader2 = sm.Subscribe("client2", new[] { "Motor.Speed" }, cts.Token);
+            var reader1 = await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
+            var reader2 = await sm.SubscribeAsync("client2", new[] { "Motor.Speed" }, cts.Token);
 
             sm.OnTagValueChanged("Motor.Speed", Vtq.Good(99.0));
 
@@ -88,11 +88,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void OnTagValueChanged_NonSubscribedTag_NoDelivery()
+        public async Task OnTagValueChanged_NonSubscribedTag_NoDelivery()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
 
             sm.OnTagValueChanged("Motor.Torque", Vtq.Good(10.0));
 
@@ -101,11 +101,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void UnsubscribeClient_CompletesChannel()
+        public async Task UnsubscribeClient_CompletesChannel()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
 
             sm.UnsubscribeClient("client1");
 
@@ -114,11 +114,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void UnsubscribeClient_RemovesFromTagSubscriptions()
+        public async Task UnsubscribeClient_RemovesFromTagSubscriptions()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
+            await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
 
             sm.UnsubscribeClient("client1");
 
@@ -128,12 +128,12 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void RefCounting_LastClientUnsubscribeRemovesTag()
+        public async Task RefCounting_LastClientUnsubscribeRemovesTag()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
-            sm.Subscribe("client2", new[] { "Motor.Speed" }, cts.Token);
+            await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
+            await sm.SubscribeAsync("client2", new[] { "Motor.Speed" }, cts.Token);
 
             sm.GetStats().TotalTags.Should().Be(1);
 
@@ -145,11 +145,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void NotifyDisconnection_SendsBadQualityToAll()
+        public async Task NotifyDisconnection_SendsBadQualityToAll()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Motor.Speed", "Motor.Torque" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Motor.Speed", "Motor.Torque" }, cts.Token);
 
             sm.NotifyDisconnection();
 
@@ -161,11 +161,11 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void Backpressure_DropOldest_DropsWhenFull()
+        public async Task Backpressure_DropOldest_DropsWhenFull()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient(), channelCapacity: 3);
             using var cts = new CancellationTokenSource();
-            var reader = sm.Subscribe("client1", new[] { "Motor.Speed" }, cts.Token);
+            var reader = await sm.SubscribeAsync("client1", new[] { "Motor.Speed" }, cts.Token);
 
             // Fill the channel beyond capacity
             for (int i = 0; i < 10; i++)
@@ -180,12 +180,12 @@ namespace ZB.MOM.WW.LmxProxy.Host.Tests.Subscriptions
         }
 
         [Fact]
-        public void GetStats_ReturnsCorrectCounts()
+        public async Task GetStats_ReturnsCorrectCounts()
         {
             using var sm = new SubscriptionManager(new FakeScadaClient());
             using var cts = new CancellationTokenSource();
-            sm.Subscribe("c1", new[] { "Tag1", "Tag2" }, cts.Token);
-            sm.Subscribe("c2", new[] { "Tag2", "Tag3" }, cts.Token);
+            await sm.SubscribeAsync("c1", new[] { "Tag1", "Tag2" }, cts.Token);
+            await sm.SubscribeAsync("c2", new[] { "Tag2", "Tag3" }, cts.Token);
 
             var stats = sm.GetStats();
             stats.TotalClients.Should().Be(2);