A interface do usuário do .NET Core 2 e SwashBuckle Swagger não está sendo exibida

Segui alguns tutoriais e consegui que isso funcionasse no trabalho, mas, por algum motivo, não consigo exibir a interface do usuário, mas o Swagger Json é criado. O último tutorial que eu olhei éaqui.

Minha configuração é assim:

Pacote de pepita: Swashbuckle.AspNetCore(1.0.0)

ConfigureServices Método:

services.AddSwaggerGen(options =>
            {
                options.SwaggerDoc("v1",
                    new Info
                    {
                        Title = "MediatR Example",
                        Version = "v1",
                        Description = "Trying out the MediatR library to simplify Request and Response logic.",
                        TermsOfService = "WTFPL",
                        Contact = new Contact
                        {
                            Email = "",
                            Name = "",
                            Url = "https://github.com/CubicleJockey/MediatR-Playground"
                        }
                    }
                );

                var xmlDocFile = Path.Combine(PlatformServices.Default.Application.ApplicationBasePath, @"MediatR-Messages.Api.xml");
                options.IncludeXmlComments(xmlDocFile);
                options.DescribeAllEnumsAsStrings();
            });

Configure Método:

 app.UseMvcWithDefaultRoute();

            // Enable middleware to serve generated Swagger as a JSON endpoint.
            app.UseSwagger();

            // Enable middleware to serve swagger-ui (HTML, JS, CSS etc.), specifying the Swagger JSON endpoint
            app.UseSwaggerUI(config =>
            {
                config.SwaggerEndpoint("/swagger/v1/swagger.json", "V1 Docs");
            });

launchSettings.json:

"IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "launchUrl": "swagger/",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },

Executar e visitar o URL JSON do Swagger produz o JSON apropriado:

   {
   "swagger":"2.0",
   "info":{
      "version":"v1",
      "title":"MediatR Example",
      "description":"Trying out the MediatR library to simplify Request and Response logic.",
      "termsOfService":"WTFPL",
      "contact":{
         "name":"André Davis",
         "url":"https://github.com/CubicleJockey/MediatR-Playground",
         "email":"[email protected]"
      }
   },
   "basePath":"/",
   "paths":{
      "/api/Addition":{
         "get":{
            "tags":[
               "Addition"
            ],
            "summary":"Get Methods that takes two numbers and gets the sum.",
            "operationId":"ApiAdditionGet",
            "consumes":[

            ],
            "produces":[
               "text/plain",
               "application/json",
               "text/json"
            ],
            "parameters":[
               {
                  "name":"left",
                  "in":"query",
                  "description":"Left hand side of the equation.",
                  "required":false,
                  "type":"integer",
                  "format":"int32"
               },
               {
                  "name":"right",
                  "in":"query",
                  "description":"Right hand side of the equation.",
                  "required":false,
                  "type":"integer",
                  "format":"int32"
               }
            ],
            "responses":{
               "200":{
                  "description":"Success",
                  "schema":{
                     "$ref":"#/definitions/Task[AdditionResponse]"
                  }
               }
            }
         }
      }
   },
   "definitions":{
      "Task[AdditionResponse]":{
         "type":"object",
         "properties":{
            "result":{
               "$ref":"#/definitions/AdditionResponse",
               "readOnly":true
            },
            "id":{
               "format":"int32",
               "type":"integer",
               "readOnly":true
            },
            "exception":{
               "type":"object",
               "readOnly":true
            },
            "status":{
               "enum":[
                  "Created",
                  "WaitingForActivation",
                  "WaitingToRun",
                  "Running",
                  "WaitingForChildrenToComplete",
                  "RanToCompletion",
                  "Canceled",
                  "Faulted"
               ],
               "type":"string",
               "readOnly":true
            },
            "isCanceled":{
               "type":"boolean",
               "readOnly":true
            },
            "isCompleted":{
               "type":"boolean",
               "readOnly":true
            },
            "isCompletedSuccessfully":{
               "type":"boolean",
               "readOnly":true
            },
            "creationOptions":{
               "enum":[
                  "None",
                  "PreferFairness",
                  "LongRunning",
                  "AttachedToParent",
                  "DenyChildAttach",
                  "HideScheduler",
                  "RunContinuationsAsynchronously"
               ],
               "type":"string",
               "readOnly":true
            },
            "asyncState":{
               "type":"object",
               "readOnly":true
            },
            "isFaulted":{
               "type":"boolean",
               "readOnly":true
            }
         }
      },
      "AdditionResponse":{
         "type":"object",
         "properties":{
            "answer":{
               "format":"int32",
               "type":"integer",
               "readOnly":true
            },
            "equation":{
               "type":"string",
               "readOnly":true
            }
         }
      }
   },
   "securityDefinitions":{

   }
}

Ao visitar o URL padrão da interface do usuário do Swagger, recebo um 404. Tentei algumas variações.

localhost: 64881 / swagger /localhost: 64881 / swagger / uilocalhost: 64881 / swagger / index.htmllocalhost: 64881 / swagger / ui / index.html

Todos os itens acima retornam 404. Eles funcionaram antes, dependendo das versões. O que estou perdendo.

Meu código-fonte completo pode ser encontrado no GitHubaqui. Este é um ramo desta pergunta, portanto o código corresponde à minha pergunta.

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