diff --git a/src/ScadaLink.CentralUI/Components/Audit/ExecutionTree.razor.cs b/src/ScadaLink.CentralUI/Components/Audit/ExecutionTree.razor.cs
index a5a5aef..c415d48 100644
--- a/src/ScadaLink.CentralUI/Components/Audit/ExecutionTree.razor.cs
+++ b/src/ScadaLink.CentralUI/Components/Audit/ExecutionTree.razor.cs
@@ -44,7 +44,11 @@ public partial class ExecutionTree
     /// Recursive — children are themselves <see cref="Subtree"/> values.
     /// </summary>
     /// <param name="Node">The execution this subtree is rooted at.</param>
-    /// <param name="Children">Child subtrees, ordered by first-occurrence time.</param>
+    /// <param name="Children">
+    /// Child subtrees, ordered by <c>(FirstOccurredAtUtc ?? DateTime.MaxValue,
+    /// ExecutionId)</c> — earliest first-occurrence time first, stub nodes
+    /// (null timestamp) last, with <c>ExecutionId</c> breaking ties.
+    /// </param>
     public sealed record Subtree(ExecutionTreeNode Node, IReadOnlyList<Subtree> Children);
 
     /// <summary>
@@ -78,6 +82,11 @@ public partial class ExecutionTree
     // or taken straight from PreBuiltRoots on a nested instance.
     private IReadOnlyList<Subtree> _rootsToRender = Array.Empty<Subtree>();
 
+    // The Nodes reference the current _rootsToRender was assembled from. Used
+    // to skip a redundant re-assembly when OnParametersSet fires for an
+    // unrelated parameter change (the flat list itself is unchanged).
+    private IReadOnlyList<ExecutionTreeNode>? _assembledFrom;
+
     // Per-execution expand/collapse state. Absent => expanded (the default):
     // the whole chain is shown on arrival so the user sees the full picture.
     private readonly HashSet<Guid> _collapsed = new();
@@ -91,15 +100,25 @@ public partial class ExecutionTree
             return;
         }
 
-        // Root instance: assemble the flat list into a tree.
-        _rootsToRender = BuildForest(Nodes ?? Array.Empty<ExecutionTreeNode>());
+        // Root instance: assemble the flat list into a tree. Re-assemble only
+        // when the Nodes reference itself changes — OnParametersSet also fires
+        // for unrelated parameter changes (e.g. ArrivedFromExecutionId), and
+        // re-running assembly then would needlessly rebuild an identical tree.
+        if (!ReferenceEquals(Nodes, _assembledFrom))
+        {
+            _assembledFrom = Nodes;
+            _rootsToRender = BuildForest(Nodes ?? Array.Empty<ExecutionTreeNode>());
+        }
     }
 
     /// <summary>
     /// Assembles the flat <see cref="ExecutionTreeNode"/> list into a forest of
     /// <see cref="Subtree"/> values. There is normally exactly one root (the
     /// chain's topmost ancestor); the method returns a list to stay total if
-    /// the input ever contains disjoint fragments.
+    /// the input ever contains disjoint fragments. A fully-cyclic feed has no
+    /// real root, so each remaining cyclic component is seeded with a fallback
+    /// root after the main pass — every execution in <paramref name="nodes"/>
+    /// is therefore placed in the forest exactly once.
     /// </summary>
     private static IReadOnlyList<Subtree> BuildForest(IReadOnlyList<ExecutionTreeNode> nodes)
     {
@@ -137,20 +156,29 @@ public partial class ExecutionTree
             }
         }
 
-        // Cycle guard: if the input is fully cyclic (A→B, B→A) every node has a
-        // present parent, so `roots` is empty even though there is data to
-        // show. Fall back to treating the lowest-ordered id as the root so the
-        // chain still renders — the visited-set below then breaks the cycle.
-        if (roots.Count == 0)
-        {
-            roots.Add(byId.Values.OrderBy(n => n.ExecutionId).First());
-        }
-
         var visited = new HashSet<Guid>();
-        return roots
+        var forest = roots
             .OrderBy(SortKey)
             .Select(root => BuildSubtree(root, childrenByParent, visited))
             .ToList();
+
+        // Cycle guard: if the input is fully cyclic every node has a present
+        // parent, so a cyclic component contributes no entry to `roots`. Any
+        // execution still missing from `visited` after the pass above belongs
+        // to such a component (a corrupt feed may contain several independent
+        // cycles, e.g. A↔B and C↔D). Seed the lowest-ordered unvisited id of
+        // each remaining component as an extra root and assemble it, looping
+        // until every node has been placed — so every execution renders.
+        while (visited.Count < byId.Count)
+        {
+            var fallbackRoot = byId.Values
+                .Where(n => !visited.Contains(n.ExecutionId))
+                .OrderBy(SortKey)
+                .First();
+            forest.Add(BuildSubtree(fallbackRoot, childrenByParent, visited));
+        }
+
+        return forest;
     }
 
     /// <summary>
@@ -231,11 +259,8 @@ public partial class ExecutionTree
         return $"{firstText} → {Iso(last)}";
     }
 
+    // Audit timestamps are UTC by system convention, so the value is formatted
+    // with a literal 'Z' suffix without re-tagging its DateTimeKind.
     private static string Iso(DateTime utc)
-    {
-        var kind = utc.Kind == DateTimeKind.Unspecified
-            ? DateTime.SpecifyKind(utc, DateTimeKind.Utc)
-            : utc;
-        return kind.ToString("yyyy-MM-dd HH:mm:ss'Z'", CultureInfo.InvariantCulture);
-    }
+        => utc.ToString("yyyy-MM-dd HH:mm:ss'Z'", CultureInfo.InvariantCulture);
 }
diff --git a/tests/ScadaLink.CentralUI.Tests/Components/Audit/ExecutionTreeTests.cs b/tests/ScadaLink.CentralUI.Tests/Components/Audit/ExecutionTreeTests.cs
index 5da931e..43b5825 100644
--- a/tests/ScadaLink.CentralUI.Tests/Components/Audit/ExecutionTreeTests.cs
+++ b/tests/ScadaLink.CentralUI.Tests/Components/Audit/ExecutionTreeTests.cs
@@ -184,6 +184,49 @@ public class ExecutionTreeTests : BunitContext
         Assert.Equal(1, CountOccurrences(cut.Markup, $"data-test=\"tree-node-{b}\""));
     }
 
+    [Fact]
+    public void ToggleExpand_CollapsesAndReExpandsChildSubtree()
+    {
+        // root → child → grandchild. Clicking the root's toggle collapses its
+        // subtree (the child node disappears); clicking it again re-expands.
+        var root = Guid.Parse("aaaaaaaa-3333-3333-3333-333333333333");
+        var child = Guid.Parse("bbbbbbbb-3333-3333-3333-333333333333");
+        var grandchild = Guid.Parse("cccccccc-3333-3333-3333-333333333333");
+        var nodes = new List<ExecutionTreeNode>
+        {
+            Node(root, null),
+            Node(child, root),
+            Node(grandchild, child),
+        };
+
+        var cut = Render<ExecutionTree>(p => p
+            .Add(c => c.Nodes, nodes)
+            .Add(c => c.ArrivedFromExecutionId, root));
+
+        // All nodes start expanded — the whole chain is visible on arrival.
+        Assert.Contains($"data-test=\"tree-node-{child}\"", cut.Markup);
+        Assert.Contains($"data-test=\"tree-node-{grandchild}\"", cut.Markup);
+
+        var toggle = cut.Find($"[data-test=\"tree-toggle-{root}\"]");
+        Assert.Equal("true", toggle.GetAttribute("aria-expanded"));
+
+        // Collapse: the child (and its descendants) must disappear.
+        toggle.Click();
+        Assert.DoesNotContain($"data-test=\"tree-node-{child}\"", cut.Markup);
+        Assert.DoesNotContain($"data-test=\"tree-node-{grandchild}\"", cut.Markup);
+        Assert.Equal(
+            "false",
+            cut.Find($"[data-test=\"tree-toggle-{root}\"]").GetAttribute("aria-expanded"));
+
+        // Re-expand: the child subtree reappears.
+        cut.Find($"[data-test=\"tree-toggle-{root}\"]").Click();
+        Assert.Contains($"data-test=\"tree-node-{child}\"", cut.Markup);
+        Assert.Contains($"data-test=\"tree-node-{grandchild}\"", cut.Markup);
+        Assert.Equal(
+            "true",
+            cut.Find($"[data-test=\"tree-toggle-{root}\"]").GetAttribute("aria-expanded"));
+    }
+
     private static int CountOccurrences(string haystack, string needle)
     {
         int count = 0, idx = 0;