diff --git a/HellionChat/MessageManager.cs b/HellionChat/MessageManager.cs
index dcb10a2..31f8b1d 100644
--- a/HellionChat/MessageManager.cs
+++ b/HellionChat/MessageManager.cs
@@ -359,12 +359,21 @@ internal class MessageManager : IAsyncDisposable
         if (Plugin.Config.DatabaseBattleMessages || !message.Code.IsBattle())
             Store.UpsertMessage(message);
 
+        // Snapshot the list, not just the active tab. This loop runs on the worker
+        // thread while SaveConfig's strip and the auto-tell spawn mutate Config.Tabs
+        // under TabsListLock — enumerating it live throws "collection was modified",
+        // and the catch in ProcessPendingMessages swallows that, silently dropping
+        // the whole message: no tab entry, no sound, no MessageProcessed.
+        List<Tab> tabsSnapshot;
+        lock (Plugin.TabsListLock)
+            tabsSnapshot = Plugin.Config.Tabs.ToList();
+
         // Snapshot the active tab and whether it shows this message ONCE, so the
         // whole loop sees a consistent value (the getter is a cross-thread read of
         // MainWindow.ActiveTab).
         var currentTab = Plugin.CurrentTab;
         var currentTabMatches = currentTab.Matches(message);
-        foreach (var tab in Plugin.Config.Tabs)
+        foreach (var tab in tabsSnapshot)
         {
             if (tab.Matches(message))
                 tab.AddMessage(message, ShouldCountUnread(tab, currentTab, currentTabMatches));
@@ -374,12 +383,24 @@ internal class MessageManager : IAsyncDisposable
         // stays pure and SelfTest-able; AddMessage above and playback below keep
         // the side effects.
         var notificationSound = SelectNotificationSound(
-            Plugin.Config.Tabs,
-            Plugin.CurrentTab,
+            tabsSnapshot,
+            currentTab,
             message,
-            Plugin.Config.PlaySounds
+            Plugin.Config.PlaySounds,
+            out var soundSource
         );
 
+        // The snapshot can outlive a tab (eviction, logout). Playing its sound would
+        // be an audible artefact for a tab that is already gone, so re-check first.
+        if (notificationSound is not null && soundSource is not null)
+        {
+            bool sourceStillPresent;
+            lock (Plugin.TabsListLock)
+                sourceStillPresent = Plugin.Config.Tabs.Contains(soundSource);
+            if (!sourceStillPresent)
+                notificationSound = null;
+        }
+
         if (notificationSound is { } soundId)
         {
             if (soundId is >= 1 and <= 16)
@@ -427,14 +448,18 @@ internal class MessageManager : IAsyncDisposable
             && currentTabMatches
         );
 
+    // Reports the tab the sound came from, so the caller can drop it if that tab
+    // disappeared between snapshot and playback.
     internal static uint? SelectNotificationSound(
         IEnumerable<Tab> tabs,
         Tab currentTab,
         Message probe,
-        bool playSounds
+        bool playSounds,
+        out Tab? source
     )
     {
         uint? picked = null;
+        source = null;
         foreach (var tab in tabs)
         {
             if (!tab.Matches(probe))
@@ -449,6 +474,7 @@ internal class MessageManager : IAsyncDisposable
             )
             {
                 picked = tab.NotificationSoundId;
+                source = tab;
             }
         }
         return picked;
@@ -460,7 +486,7 @@ internal class MessageManager : IAsyncDisposable
         Tab currentTab,
         Message probe,
         bool playSounds
-    ) => SelectNotificationSound(tabs, currentTab, probe, playSounds);
+    ) => SelectNotificationSound(tabs, currentTab, probe, playSounds, out _);
 
     internal class NameFormatting
     {