diff --git a/agent/ShopDbEndpointAgent.Tray/FleetAlertForm.cs b/agent/ShopDbEndpointAgent.Tray/FleetAlertForm.cs
index a838f434..4b88913d 100644
--- a/agent/ShopDbEndpointAgent.Tray/FleetAlertForm.cs
+++ b/agent/ShopDbEndpointAgent.Tray/FleetAlertForm.cs
@@ -68,26 +68,33 @@ internal sealed class FleetAlertForm : Form
         statusCheckTimer.Start();
     }
 
-    private async void StatusCheckTimer_Tick(object? sender, EventArgs e)
+    private void StatusCheckTimer_Tick(object? sender, EventArgs e)
     {
         if (client == null || hostname == null)
             return;
 
-        try
+        Task.Run(async () =>
         {
-            var alerts = await client.FetchAlertsAsync(hostname, CancellationToken.None);
-            var stillActive = alerts?.Any(a => a.NotificationId == alert.NotificationId) ?? false;
-
-            if (!stillActive)
+            try
             {
-                statusCheckTimer?.Stop();
-                Close();
+                var alerts = await client.FetchAlertsAsync(hostname, CancellationToken.None)
+                    .ConfigureAwait(false);
+                var stillActive = alerts?.Any(a => a.NotificationId == alert.NotificationId) ?? false;
+
+                if (!stillActive)
+                {
+                    BeginInvoke(new Action(() =>
+                    {
+                        statusCheckTimer?.Stop();
+                        Close();
+                    }));
+                }
             }
-        }
-        catch
-        {
-            // Ignore errors - keep the form open if we can't check status
-        }
+            catch
+            {
+                // Ignore errors - keep the form open if we can't check status
+            }
+        });
     }
 
     private void ApplyRoundedCorners()
diff --git a/agent/ShopDbEndpointAgent.Tray/FleetAlertWorker.cs b/agent/ShopDbEndpointAgent.Tray/FleetAlertWorker.cs
index d097b3fb..d9ec6a69 100644
--- a/agent/ShopDbEndpointAgent.Tray/FleetAlertWorker.cs
+++ b/agent/ShopDbEndpointAgent.Tray/FleetAlertWorker.cs
@@ -159,24 +159,25 @@ internal sealed class FleetAlertWorker : IDisposable
 
     private void OnAlertAcknowledged(FleetAlert alert, CancellationToken token)
     {
-        try
-        {
-            logger.LogInformation(
-                "Fleet alert {NotificationId} acknowledged; posting to server.", alert.NotificationId);
+        logger.LogInformation(
+            "Fleet alert {NotificationId} acknowledged; queuing server post.", alert.NotificationId);
 
-            client.AcknowledgeAlertAsync(alert.NotificationId, assetId, hostname, token)
-                .GetAwaiter()
-                .GetResult();
+        store.MarkAcknowledged(alert.NotificationId);
 
-            store.MarkAcknowledged(alert.NotificationId);
-            logger.LogInformation("Fleet alert {NotificationId} recorded.", alert.NotificationId);
-        }
-        catch (Exception exception)
+        Task.Run(async () =>
         {
-            logger.LogWarning(exception,
-                "Could not acknowledge fleet alert {NotificationId}; will retry on next poll.",
-                alert.NotificationId);
-        }
+            try
+            {
+                await client.AcknowledgeAlertAsync(alert.NotificationId, assetId, hostname, token);
+                logger.LogInformation("Fleet alert {NotificationId} posted to server.", alert.NotificationId);
+            }
+            catch (Exception exception)
+            {
+                logger.LogWarning(exception,
+                    "Could not post acknowledgment for fleet alert {NotificationId}; already marked locally.",
+                    alert.NotificationId);
+            }
+        });
     }
 
     public void Dispose()
diff --git a/agent/ShopDbEndpointAgent.Tray/ShopDbEndpointAgent.Tray.csproj b/agent/ShopDbEndpointAgent.Tray/ShopDbEndpointAgent.Tray.csproj
index 9b788fff..4c2e0398 100644
--- a/agent/ShopDbEndpointAgent.Tray/ShopDbEndpointAgent.Tray.csproj
+++ b/agent/ShopDbEndpointAgent.Tray/ShopDbEndpointAgent.Tray.csproj
@@ -79,7 +79,10 @@
 	<!-- 1.6.3: auto-close when notification becomes inactive. Fleet alert forms now
 	     check every 30 seconds if the notification is still active on the server and
 	     automatically close if it has ended or been deactivated. -->
-	<Version>1.6.3</Version>
+	<!-- 1.6.4: fix UI thread deadlock. Acknowledgment and status checks now run async
+	     properly without blocking the UI thread. Acknowledgment is marked locally first,
+	     then posted to server in background to prevent lockups. -->
+	<Version>1.6.4</Version>
 	<InvariantGlobalization>true</InvariantGlobalization>
 	<RuntimeIdentifier>win-x64</RuntimeIdentifier>
 	<SelfContained>true</SelfContained>
diff --git a/agent/ShopDbEndpointAgent/ShopDbEndpointAgent.csproj b/agent/ShopDbEndpointAgent/ShopDbEndpointAgent.csproj
index 6e853e28..1400b34b 100644
--- a/agent/ShopDbEndpointAgent/ShopDbEndpointAgent.csproj
+++ b/agent/ShopDbEndpointAgent/ShopDbEndpointAgent.csproj
@@ -175,7 +175,9 @@
 	     No agent code changes, but deployed together for version consistency. -->
 	<!-- 1.13.2: coordinated release with tray 1.6.3 (auto-close when inactive, crash fix).
 	     No agent code changes, but deployed together for version consistency. -->
-	<Version>1.13.2</Version>
+	<!-- 1.13.3: coordinated release with tray 1.6.4 (deadlock fix).
+	     No agent code changes, but deployed together for version consistency. -->
+	<Version>1.13.3</Version>
 	<InvariantGlobalization>true</InvariantGlobalization>
 	<RuntimeIdentifier>win-x64</RuntimeIdentifier>
 	<SelfContained>true</SelfContained>