diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
index 985a6aab..a358d7d7 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
@@ -1576,31 +1576,38 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
     ///     served Equipment address space (Tasks 4/5), an attribute notification alone is invisible to a
     ///     subscribed client — only a model-change event tells it the address space grew.
     ///     <para>
-    ///         Built AND reported under <c>Lock</c> (like <see cref="ReportConditionEvent"/>) and wrapped in
-    ///         try/catch so it is tolerant when eventing is disabled / there are no monitored items / the
-    ///         server is shutting down — the same swallow-and-log tolerance as the write-revert path
-    ///         (<see cref="ReportAuditEvent"/>). The nodes have already been materialised, so a surprise from
-    ///         the event path MUST NOT propagate out of this announcement.
+    ///         The event is built under <c>Lock</c> but reported AFTER the lock is released, mirroring
+    ///         <see cref="ReportNodeShapeChangedEvent"/> / <see cref="RevertOptimisticWriteIfNeeded"/>:
+    ///         <c>Server.ReportEvent</c> re-enters the server's own subscription/event path, so holding the node
+    ///         <c>Lock</c> across it risks a lock-order inversion with a client that has event subscriptions.
+    ///         The report is wrapped in try/catch so it is tolerant when eventing is disabled / there are no
+    ///         monitored items / the server is shutting down — the same swallow-and-log tolerance as the
+    ///         write-revert path (<see cref="ReportAuditEvent"/>). The nodes have already been materialised, so
+    ///         a surprise from the event path MUST NOT propagate out of this announcement.
     ///     </para>
     /// </summary>
     /// <param name="affectedNodeId">The folder-scoped node id of the parent under which nodes were added.</param>
     public void RaiseNodesAddedModelChange(string affectedNodeId)
     {
         ArgumentException.ThrowIfNullOrEmpty(affectedNodeId);
+        GeneralModelChangeEventState e;
         lock (Lock)
         {
-            try
-            {
-                Server.ReportEvent(SystemContext, BuildNodesAddedModelChange(affectedNodeId));
-            }
-            catch (Exception ex)
-            {
-                // Model-change reporting disabled / no monitored items / server shutting down ⇒ ReportEvent may
-                // no-op or throw; either way the node add already stands. Log to the SDK trace, don't rethrow.
+            e = BuildNodesAddedModelChange(affectedNodeId);
+        }
+        // Report OUTSIDE Lock — Server.ReportEvent re-enters the server's own subscription/event path; holding
+        // Lock across it risks a lock-order inversion (mirrors ReportNodeShapeChangedEvent).
+        try
+        {
+            Server.ReportEvent(SystemContext, e);
+        }
+        catch (Exception ex)
+        {
+            // Model-change reporting disabled / no monitored items / server shutting down ⇒ ReportEvent may
+            // no-op or throw; either way the node add already stands. Log to the SDK trace, don't rethrow.
 #pragma warning disable CS0618 // Utils.LogError is [Obsolete] in favour of an ITelemetryContext this manager doesn't carry.
-                Utils.LogError(ex, "OtOpcUaNodeManager: failed to report GeneralModelChangeEvent(NodeAdded) for {0}", affectedNodeId);
+            Utils.LogError(ex, "OtOpcUaNodeManager: failed to report GeneralModelChangeEvent(NodeAdded) for {0}", affectedNodeId);
 #pragma warning restore CS0618
-            }
         }
     }
 
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerModelChangeOnAddTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerModelChangeOnAddTests.cs
index 1801794b..7b942b55 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerModelChangeOnAddTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerModelChangeOnAddTests.cs
@@ -60,6 +60,30 @@ public sealed class NodeManagerModelChangeOnAddTests : IDisposable
         await host.DisposeAsync();
     }
 
+    /// <summary>For an affected id that is not (yet) materialised, the built event still announces NodeAdded but
+    /// its AffectedType falls back to <see cref="NodeId.Null"/> (a valid Part 3 "type not applicable") — the
+    /// documented fallback of <see cref="OtOpcUaNodeManager.BuildNodesAddedModelChange"/>, locked in as an
+    /// invariant.</summary>
+    [Trait("Category", "Unit")]
+    [Fact]
+    public async Task Built_event_for_unknown_id_falls_back_to_null_AffectedType()
+    {
+        var (host, server) = await BootAsync();
+        var nm = server.NodeManager!;
+
+        // No EnsureFolder/EnsureVariable for this id — it is not in the node maps.
+        var e = nm.BuildNodesAddedModelChange("eq-unknown");
+
+        e.ShouldNotBeNull();
+        e.Changes.ShouldNotBeNull();
+        var changes = e.Changes.Value;
+        changes.Length.ShouldBe(1);
+        changes[0].Verb.ShouldBe((byte)ModelChangeStructureVerbMask.NodeAdded);
+        changes[0].AffectedType.ShouldBe(NodeId.Null);
+
+        await host.DisposeAsync();
+    }
+
     /// <summary>Raising the announcement is tolerant: callable before any nodes exist (unknown affected id ⇒
     /// AffectedType defaults to null, still a valid Part 3 change) AND after they are materialised, and never
     /// throws even when the event path reaches no monitored items (same tolerance as the write-revert path).</summary>