diff --git a/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor b/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
index b5ff6a1..0866097 100644
--- a/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
+++ b/src/ScadaLink.CentralUI/Components/Shared/TreeView.razor
@@ -32,7 +32,7 @@ else
         var key = KeySelector(item);
         var children = ChildrenSelector(item);
         var isBranch = HasChildrenSelector(item);
-        var isExpanded = _expandedKeys.Contains(key);
+        var isExpanded = _expandedKeys.Contains(KeyStr(key));
 
         <li role="treeitem" @key="key"
             aria-expanded="@(isBranch ? (isExpanded ? "true" : "false") : null)"
@@ -66,7 +66,10 @@ else
 
 @code {
     private IReadOnlyList<TItem>? _items;
-    private HashSet<object> _expandedKeys = new();
+    private HashSet<string> _expandedKeys = new();
+
+    /// <summary>Normalize any key object to a string for consistent comparison with sessionStorage.</summary>
+    private string KeyStr(object key) => key.ToString()!;
     private bool _initialExpansionApplied;
     private bool _storageLoaded;
     private TItem? _contextMenuItem;
@@ -124,7 +127,7 @@ else
                 var keys = System.Text.Json.JsonSerializer.Deserialize<List<string>>(json);
                 if (keys != null)
                 {
-                    _expandedKeys = new HashSet<object>(keys);
+                    _expandedKeys = new HashSet<string>(keys);
                     _initialExpansionApplied = true;
                 }
             }
@@ -159,7 +162,7 @@ else
         {
             if (InitiallyExpanded!(item))
             {
-                _expandedKeys.Add(KeySelector(item));
+                _expandedKeys.Add(KeyStr(KeySelector(item)));
             }
 
             var children = ChildrenSelector(item);
@@ -172,9 +175,10 @@ else
 
     private void ToggleExpand(object key)
     {
-        if (!_expandedKeys.Remove(key))
+        var k = KeyStr(key);
+        if (!_expandedKeys.Remove(k))
         {
-            _expandedKeys.Add(key);
+            _expandedKeys.Add(k);
         }
 
         PersistExpandedState();
@@ -184,8 +188,7 @@ else
     {
         if (StorageKey != null)
         {
-            var keys = _expandedKeys.Select(k => k.ToString()!).ToList();
-            var json = System.Text.Json.JsonSerializer.Serialize(keys);
+            var json = System.Text.Json.JsonSerializer.Serialize(_expandedKeys.ToList());
             _ = JSRuntime.InvokeVoidAsync("treeviewStorage.save", StorageKey, json);
         }
     }
@@ -232,7 +235,7 @@ else
         {
             if (HasChildrenSelector(item))
             {
-                _expandedKeys.Add(KeySelector(item));
+                _expandedKeys.Add(KeyStr(KeySelector(item)));
             }
 
             var children = ChildrenSelector(item);
@@ -258,13 +261,14 @@ else
     public async Task RevealNode(object key, bool select = false)
     {
         var parentLookup = BuildParentLookup();
+        var k = KeyStr(key);
 
         // If key is not in the tree at all, no-op
-        if (!parentLookup.ContainsKey(key))
+        if (!parentLookup.ContainsKey(k))
             return;
 
         // Walk up through ancestors
-        var current = key;
+        var current = k;
         while (parentLookup.TryGetValue(current, out var parentKey) && parentKey != null)
         {
             _expandedKeys.Add(parentKey);
@@ -280,9 +284,9 @@ else
         StateHasChanged();
     }
 
-    private Dictionary<object, object?> BuildParentLookup()
+    private Dictionary<string, string?> BuildParentLookup()
     {
-        var lookup = new Dictionary<object, object?>();
+        var lookup = new Dictionary<string, string?>();
         if (_items is { Count: > 0 })
         {
             BuildParentLookupRecursive(_items, null, lookup);
@@ -290,11 +294,11 @@ else
         return lookup;
     }
 
-    private void BuildParentLookupRecursive(IReadOnlyList<TItem> items, object? parentKey, Dictionary<object, object?> lookup)
+    private void BuildParentLookupRecursive(IReadOnlyList<TItem> items, string? parentKey, Dictionary<string, string?> lookup)
     {
         foreach (var item in items)
         {
-            var key = KeySelector(item);
+            var key = KeyStr(KeySelector(item));
             lookup[key] = parentKey;
 
             var children = ChildrenSelector(item);