diff --git a/src/modules/Elsa.Common/Multitenancy/Implementations/DefaultTenantService.cs b/src/modules/Elsa.Common/Multitenancy/Implementations/DefaultTenantService.cs
index 9db13dc361..fca84ebc97 100644
--- a/src/modules/Elsa.Common/Multitenancy/Implementations/DefaultTenantService.cs
+++ b/src/modules/Elsa.Common/Multitenancy/Implementations/DefaultTenantService.cs
@@ -5,12 +5,15 @@ namespace Elsa.Common.Multitenancy;
 public class DefaultTenantService(IServiceScopeFactory scopeFactory, ITenantScopeFactory tenantScopeFactory, TenantEventsManager tenantEvents, ITenantAccessor tenantAccessor) : ITenantService, IAsyncDisposable
 {
     private readonly AsyncServiceScope _serviceScope = scopeFactory.CreateAsyncScope();
+    private readonly SemaphoreSlim _initializationLock = new(1, 1);
+    private readonly SemaphoreSlim _refreshLock = new(1, 1);
     private IDictionary<string, Tenant>? _tenantsDictionary;
     private IDictionary<Tenant, TenantScope>? _tenantScopesDictionary;
 
     public async ValueTask DisposeAsync()
     {
         await _serviceScope.DisposeAsync();
+        _initializationLock.Dispose();
     }
 
     public async Task<Tenant?> FindAsync(string id, CancellationToken cancellationToken = default)
@@ -56,7 +59,8 @@ public async Task ActivateTenantsAsync(CancellationToken cancellationToken = def
 
     public async Task DeactivateTenantsAsync(CancellationToken cancellationToken = default)
     {
-        var tenants = _tenantsDictionary!.Values.ToArray();
+        var dictionary = await GetTenantsDictionaryAsync(cancellationToken);
+        var tenants = dictionary.Values.ToArray();
 
         foreach (var tenant in tenants)
             await UnregisterTenantAsync(tenant, cancellationToken);
@@ -64,25 +68,34 @@ public async Task DeactivateTenantsAsync(CancellationToken cancellationToken = d
 
     public async Task RefreshAsync(CancellationToken cancellationToken = default)
     {
-        await using var scope = scopeFactory.CreateAsyncScope();
-        var tenantsProvider = scope.ServiceProvider.GetRequiredService<ITenantsProvider>();
-        var currentTenants = await GetTenantsDictionaryAsync(cancellationToken);
-        var currentTenantIds = currentTenants.Keys;
-        var newTenants = (await tenantsProvider.ListAsync(cancellationToken)).ToDictionary(x => x.Id);
-        var newTenantIds = newTenants.Keys;
-        var removedTenantIds = currentTenantIds.Except(newTenantIds).ToArray();
-        var addedTenantIds = newTenantIds.Except(currentTenantIds).ToArray();
-
-        foreach (var removedTenantId in removedTenantIds)
+        await _refreshLock.WaitAsync(cancellationToken);
+
+        try
         {
-            var removedTenant = currentTenants[removedTenantId];
-            await UnregisterTenantAsync(removedTenant, cancellationToken);
+            await using var scope = scopeFactory.CreateAsyncScope();
+            var tenantsProvider = scope.ServiceProvider.GetRequiredService<ITenantsProvider>();
+            var currentTenants = await GetTenantsDictionaryAsync(cancellationToken);
+            var currentTenantIds = currentTenants.Keys;
+            var newTenants = (await tenantsProvider.ListAsync(cancellationToken)).ToDictionary(x => x.Id);
+            var newTenantIds = newTenants.Keys;
+            var removedTenantIds = currentTenantIds.Except(newTenantIds).ToArray();
+            var addedTenantIds = newTenantIds.Except(currentTenantIds).ToArray();
+
+            foreach (var removedTenantId in removedTenantIds)
+            {
+                var removedTenant = currentTenants[removedTenantId];
+                await UnregisterTenantAsync(removedTenant, cancellationToken);
+            }
+
+            foreach (var addedTenantId in addedTenantIds)
+            {
+                var addedTenant = newTenants[addedTenantId];
+                await RegisterTenantAsync(addedTenant, cancellationToken);
+            }
         }
-
-        foreach (var addedTenantId in addedTenantIds)
+        finally
         {
-            var addedTenant = newTenants[addedTenantId];
-            await RegisterTenantAsync(addedTenant, cancellationToken);
+            _refreshLock.Release();
         }
     }
 
@@ -90,13 +103,24 @@ private async Task<IDictionary<string, Tenant>> GetTenantsDictionaryAsync(Cancel
     {
         if (_tenantsDictionary == null)
         {
-            _tenantsDictionary = new Dictionary<string, Tenant>();
-            _tenantScopesDictionary = new Dictionary<Tenant, TenantScope>();
-            var tenantsProvider = _serviceScope.ServiceProvider.GetRequiredService<ITenantsProvider>();
-            var tenants = await tenantsProvider.ListAsync(cancellationToken);
-
-            foreach (var tenant in tenants)
-                await RegisterTenantAsync(tenant, cancellationToken);
+            await _initializationLock.WaitAsync(cancellationToken); // Lock to ensure single-threaded initialization
+            try
+            {
+                if (_tenantsDictionary == null) // Double-check locking
+                {
+                    _tenantsDictionary = new Dictionary<string, Tenant>();
+                    _tenantScopesDictionary = new Dictionary<Tenant, TenantScope>();
+                    var tenantsProvider = _serviceScope.ServiceProvider.GetRequiredService<ITenantsProvider>();
+                    var tenants = await tenantsProvider.ListAsync(cancellationToken);
+
+                    foreach (var tenant in tenants)
+                        await RegisterTenantAsync(tenant, cancellationToken);
+                }
+            }
+            finally
+            {
+                _initializationLock.Release();
+            }
         }
 
         return _tenantsDictionary;
@@ -114,11 +138,12 @@ private async Task RegisterTenantAsync(Tenant tenant, CancellationToken cancella
 
     private async Task UnregisterTenantAsync(Tenant tenant, CancellationToken cancellationToken = default)
     {
-        var scope = _tenantScopesDictionary![tenant];
-        _tenantsDictionary!.Remove(tenant.Id);
-        _tenantScopesDictionary!.Remove(tenant);
+        if (_tenantScopesDictionary!.Remove(tenant, out var scope))
+        {
+            _tenantsDictionary!.Remove(tenant.Id, out _);
 
-        using (tenantAccessor.PushContext(tenant))
-            await tenantEvents.TenantDeactivatedAsync(new TenantDeactivatedEventArgs(tenant, scope, cancellationToken));
+            using (tenantAccessor.PushContext(tenant))
+                await tenantEvents.TenantDeactivatedAsync(new TenantDeactivatedEventArgs(tenant, scope, cancellationToken));
+        }
     }
 }
\ No newline at end of file
diff --git a/src/modules/Elsa.Tenants.AspNetCore/Extensions/ModuleExtensions.cs b/src/modules/Elsa.Tenants.AspNetCore/Extensions/ModuleExtensions.cs
index a098277e0c..45b54a672e 100644
--- a/src/modules/Elsa.Tenants.AspNetCore/Extensions/ModuleExtensions.cs
+++ b/src/modules/Elsa.Tenants.AspNetCore/Extensions/ModuleExtensions.cs
@@ -13,7 +13,7 @@ public static class ModuleExtensions
     /// <summary>
     /// Installs and configures the <see cref="TenantsFeature"/> feature.
     /// </summary>
-    public static IModule UseTenantHttpRouting(this IModule module, Action<MultitenantHttpRoutingFeature>? configure = default)
+    public static IModule UseTenantHttpRouting(this IModule module, Action<MultitenantHttpRoutingFeature>? configure = null)
     {
         module.Configure(configure);
         return module;