diff --git a/.github/workflows/ReleaseNotes.md b/.github/workflows/ReleaseNotes.md
index 13664446c..b5b84be15 100644
--- a/.github/workflows/ReleaseNotes.md
+++ b/.github/workflows/ReleaseNotes.md
@@ -8,4 +8,5 @@
 * [Client] Exposed more TLS options (#1729).
 * [Client] Fixed wrong return code conversion (#1729).
 * [Server] Improved performance by changing internal locking strategy for subscriptions (#1716, thanks to @zeheng).
+* [Server] Fixed exceptions when clients are connecting and disconnecting very fast while accessing the client status for connection validation (#1742).
 * [Server] Exposed more properties in _ClientConnectedEventArgs_ (#1738).
diff --git a/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs b/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
index 0c16fd4b4..c0d385d63 100644
--- a/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
+++ b/Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs
@@ -58,7 +58,7 @@ public MqttClientSessionsManager(
             _eventContainer = eventContainer ?? throw new ArgumentNullException(nameof(eventContainer));
         }
 
-        public async Task CloseAllConnectionsAsync()
+        public async Task CloseAllConnections()
         {
             List<MqttClient> connections;
             lock (_clients)
@@ -306,17 +306,17 @@ public List<MqttClient> GetClients()
             }
         }
 
-        public Task<IList<MqttClientStatus>> GetClientStatusesAsync()
+        public Task<IList<MqttClientStatus>> GetClientsStatus()
         {
             var result = new List<MqttClientStatus>();
 
             lock (_clients)
             {
-                foreach (var connection in _clients.Values)
+                foreach (var client in _clients.Values)
                 {
-                    var clientStatus = new MqttClientStatus(connection)
+                    var clientStatus = new MqttClientStatus(client)
                     {
-                        Session = new MqttSessionStatus(connection.Session)
+                        Session = new MqttSessionStatus(client.Session)
                     };
 
                     result.Add(clientStatus);
@@ -326,7 +326,7 @@ public Task<IList<MqttClientStatus>> GetClientStatusesAsync()
             return Task.FromResult((IList<MqttClientStatus>)result);
         }
 
-        public Task<IList<MqttSessionStatus>> GetSessionStatusAsync()
+        public Task<IList<MqttSessionStatus>> GetSessionsStatus()
         {
             var result = new List<MqttSessionStatus>();
 
@@ -614,20 +614,15 @@ async Task<MqttClient> CreateClientConnection(
                     // Create a new client (always required).
                     lock (_clients)
                     {
-                        _clients.TryGetValue(connectPacket.ClientId, out oldClient);    
-                    }
-                    
-                    if (oldClient != null)
-                    {
-                        // This will stop the current client from sending and receiving but remains the connection active
-                        // for a later DISCONNECT packet.
-                        oldClient.IsTakenOver = true;
-                    }
-
-                    client = CreateClient(connectPacket, channelAdapter, session);
+                        _clients.TryGetValue(connectPacket.ClientId, out oldClient);
+                        if (oldClient != null)
+                        {
+                            // This will stop the current client from sending and receiving but remains the connection active
+                            // for a later DISCONNECT packet.
+                            oldClient.IsTakenOver = true;
+                        }
 
-                    lock (_clients)
-                    {
+                        client = CreateClient(connectPacket, channelAdapter, session);
                         _clients[connectPacket.ClientId] = client;
                     }
                 }
diff --git a/Source/MQTTnet/Server/MqttServer.cs b/Source/MQTTnet/Server/MqttServer.cs
index daed20556..ff6c806e0 100644
--- a/Source/MQTTnet/Server/MqttServer.cs
+++ b/Source/MQTTnet/Server/MqttServer.cs
@@ -200,7 +200,7 @@ public Task<IList<MqttClientStatus>> GetClientsAsync()
         {
             ThrowIfNotStarted();
 
-            return _clientSessionsManager.GetClientStatusesAsync();
+            return _clientSessionsManager.GetClientsStatus();
         }
 
         public Task<IList<MqttApplicationMessage>> GetRetainedMessagesAsync()
@@ -226,7 +226,7 @@ public Task<IList<MqttSessionStatus>> GetSessionsAsync()
         {
             ThrowIfNotStarted();
 
-            return _clientSessionsManager.GetSessionStatusAsync();
+            return _clientSessionsManager.GetSessionsStatus();
         }
 
         public Task InjectApplicationMessage(InjectedMqttApplicationMessage injectedApplicationMessage, CancellationToken cancellationToken = default)
@@ -292,7 +292,7 @@ public async Task StopAsync()
 
                 _cancellationTokenSource.Cancel(false);
 
-                await _clientSessionsManager.CloseAllConnectionsAsync().ConfigureAwait(false);
+                await _clientSessionsManager.CloseAllConnections().ConfigureAwait(false);
 
                 foreach (var adapter in _adapters)
                 {