diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OpcUaApplicationHost.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OpcUaApplicationHost.cs
index 6a806fab..73272688 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OpcUaApplicationHost.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OpcUaApplicationHost.cs
@@ -173,6 +173,9 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     private ApplicationInstance? _application;
     private StandardServer? _server;
     private ImpersonateEventHandler? _impersonateHandler;
+    private readonly object _lifetimeLock = new();
+    private readonly TaskCompletionSource _disposeCompletion = new(TaskCreationOptions.RunContinuationsAsynchronously);
+    private int _disposeStarted;
 
     /// <summary>Initializes a new instance of the OPC UA application host.</summary>
     /// <param name="options">The host configuration options.</param>
@@ -200,16 +203,18 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task StartAsync(StandardServer server, CancellationToken cancellationToken)
     {
-        _server = server;
-        // 1.5.378 requires an ITelemetryContext on the ApplicationInstance ctor (the parameterless ctor
-        // is obsolete). DefaultTelemetry.Create wires the SDK's internal logging; an empty builder keeps
-        // the SDK's trace off our ILogger (the host keeps its own _logger) — sufficient for the bootstrap.
-        _application = new ApplicationInstance(DefaultTelemetry.Create(_ => { }))
+        lock (_lifetimeLock)
         {
-            ApplicationName = _options.ApplicationName,
-            ApplicationType = ApplicationType.Server,
-            ConfigSectionName = "OtOpcUa",
-        };
+            ObjectDisposedException.ThrowIf(Volatile.Read(ref _disposeStarted) != 0, this);
+            _server = server;
+            // 1.5.378 requires telemetry on ApplicationInstance; the empty builder keeps SDK tracing separate.
+            _application = new ApplicationInstance(DefaultTelemetry.Create(_ => { }))
+            {
+                ApplicationName = _options.ApplicationName,
+                ApplicationType = ApplicationType.Server,
+                ConfigSectionName = "OtOpcUa",
+            };
+        }
 
         _ = await BuildConfigurationAsync(cancellationToken);
         await EnsureApplicationCertificateAsync(cancellationToken).ConfigureAwait(false);
@@ -657,25 +662,60 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
 
     /// <summary>Disposes the application host and cleans up resources.</summary>
     /// <returns>A task that represents the asynchronous operation.</returns>
-    public async ValueTask DisposeAsync()
+    public ValueTask DisposeAsync()
     {
+        if (Interlocked.CompareExchange(ref _disposeStarted, 1, 0) == 0)
+            _ = CompleteDisposalAsync();
+        return new ValueTask(_disposeCompletion.Task);
+    }
+
+    private async Task CompleteDisposalAsync()
+    {
+        Exception? failure = null;
         try
         {
-            // An explicit SDK stop may already have halted CurrentInstance; still continue disposal.
-            if (_impersonateHandler is not null && _server?.CurrentInstance?.SessionManager is { } sessionManager)
-                sessionManager.ImpersonateUser -= _impersonateHandler;
-        }
-        catch (Exception ex)
-        {
-            _logger.LogWarning(ex, "OpcUaApplicationHost: detaching ImpersonateUser threw");
-        }
-        _impersonateHandler = null;
+            ApplicationInstance? application;
+            StandardServer? server;
+            ImpersonateEventHandler? handler;
+            lock (_lifetimeLock)
+            {
+                application = _application;
+                server = _server;
+                handler = _impersonateHandler;
+                _application = null;
+                _server = null;
+                _impersonateHandler = null;
+            }
 
-        if (_application is not null)
+            try
+            {
+                try
+                {
+                    // An explicit SDK stop may already have halted CurrentInstance; terminal disposal still follows.
+                    if (handler is not null && server?.CurrentInstance?.SessionManager is { } sessionManager)
+                        sessionManager.ImpersonateUser -= handler;
+                }
+                catch (Exception ex) { _logger.LogWarning(ex, "OpcUaApplicationHost: detaching ImpersonateUser threw"); }
+
+                if (application is not null)
+                {
+                    try { await application.StopAsync().ConfigureAwait(false); }
+                    catch (Exception ex) { _logger.LogWarning(ex, "OpcUaApplicationHost: Stop threw on dispose"); }
+                }
+            }
+            finally
+            {
+                // SDK1 Stop does not release the server's request queue or terminal event registrations (#807).
+                try { server?.Dispose(); }
+                catch (Exception ex) { _logger.LogWarning(ex, "OpcUaApplicationHost: server disposal threw"); }
+            }
+        }
+        catch (Exception error) { failure = error; }
+        finally
         {
-            // 1.5.378: ApplicationInstance.Stop() → StopAsync().
-            try { await _application.StopAsync().ConfigureAwait(false); }
-            catch (Exception ex) { _logger.LogWarning(ex, "OpcUaApplicationHost: Stop threw on dispose"); }
+            // All callers observe completion, including when a logger or cleanup callback throws.
+            if (failure is null) _disposeCompletion.TrySetResult();
+            else _disposeCompletion.TrySetException(failure);
         }
     }
 }