For now, we explicitly require AddDistributedCache in Startup so it's not called twice.

src/Umbraco.Web.BackOffice/DependencyInjection/UmbracoBuilderExtensions.cs

@@ -43,8 +43,7 @@ namespace Umbraco.Web.BackOffice.DependencyInjection
                 .AddMvcAndRazor()
                 .AddWebServer()
                 .AddPreviewSupport()
-                .AddHostedServices()
-                .AddDistributedCache();
+                .AddHostedServices();
 
         /// <summary>
         /// Adds Umbraco back office authentication requirements

src/Umbraco.Web.UI.NetCore/Startup.cs

@@ -6,6 +6,7 @@ using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Umbraco.Core.DependencyInjection;
 using Umbraco.Extensions;
+using Umbraco.Infrastructure.DependencyInjection;
 using Umbraco.Web.BackOffice.DependencyInjection;
 using Umbraco.Web.BackOffice.Security;
 using Umbraco.Web.Common.DependencyInjection;
@@ -47,6 +48,7 @@ namespace Umbraco.Web.UI.NetCore
             services.AddUmbraco(_env, _config)
                 .AddBackOffice()
                 .AddWebsite()
+                .AddDistributedCache()
                 .AddComposers()
                 .Build();
 #pragma warning restore IDE0022 // Use expression body for methods

src/Umbraco.Web.Website/DependencyInjection/UmbracoBuilderExtensions.cs

@@ -43,8 +43,6 @@ namespace Umbraco.Web.Website.DependencyInjection
             builder.Services.AddScoped<UmbracoRouteValueTransformer>();
             builder.Services.AddSingleton<IUmbracoRenderingDefaults, UmbracoRenderingDefaults>();
 
-            builder.AddDistributedCache();
-
             return builder;
         }