diff --git a/src/TeamsISO.App/ViewModels/MainViewModel.cs b/src/TeamsISO.App/ViewModels/MainViewModel.cs
index b5730de..af785b9 100644
--- a/src/TeamsISO.App/ViewModels/MainViewModel.cs
+++ b/src/TeamsISO.App/ViewModels/MainViewModel.cs
@@ -346,10 +346,18 @@ public sealed class MainViewModel : ObservableObject, IDisposable
         // Apply the operator's saved sort preference, if any.
         ApplySortFromPrefs();
 
+        // Subscribe directly (no ObserveOn) and marshal to the UI thread inside
+        // the callback via Dispatcher.InvokeAsync. The previous ObserveOn(
+        // SynchronizationContextScheduler) path captured SynchronizationContext
+        // .Current at subscribe time — fragile in WPF startup ordering, where
+        // the UI thread's SyncContext can be in a transitional state during
+        // App.OnStartup and the captured context never pumps subsequent
+        // OnNext calls. Direct subscribe + explicit dispatcher marshal is the
+        // pattern proven by Console.Program.cs (engine emits, consumer marshals).
         _participantsSub = controller.Participants
-            .ObserveOn(new SynchronizationContextScheduler(
-                System.Threading.SynchronizationContext.Current ?? new DispatcherSynchronizationContext(_dispatcher)))
-            .Subscribe(OnParticipantsChanged);
+            .Subscribe(snapshot => _dispatcher.InvokeAsync(
+                () => OnParticipantsChanged(snapshot),
+                DispatcherPriority.Background));
 
         _alertsSub = controller.Alerts
             .ObserveOn(new SynchronizationContextScheduler(