Failed to load API definition. Fetch error. Not Found /swagger/v1/swagger.json

[Exagram]

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1. If it's not a bug report, feature request or PR, don't submit it here. Post to Stackoverflow instead.
2. If your issue is specifically a UI concern, don't submit it here. Post to the swagger-ui repo.
3. For bug reports, specify the version you're using and provide clear repro steps.

Swashbuckle Version 6.2.3.

Steps:

• In Visual Studio debug the project.
• Navigate to localhost:12345/swagger
• Observe "LOADING" for a few minutes
• After a few minutes observe: Failed to load API definition. Fetch Error. Not Found /swagger/v1/swagger.json

startup.cs

            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new OpenApiInfo
                {
                    Version = "v1",
                    Title = "...",
                    Description = "...",
                    Contact = new OpenApiContact
                    {
                        Name = "...",
                        Email = "[email protected]",
                        Url = new Uri("https://...")
                    }
                });

                var xmlFile = $"{Assembly.GetExecutingAssembly().GetName().Name}.xml";
                var xmlPath = Path.Combine(AppContext.BaseDirectory, xmlFile);
                c.IncludeXmlComments(xmlPath);
            });

...

                app.UseDeveloperExceptionPage();
                app.UseSwagger();
                app.UseSwaggerUI(c =>
                {
                    c.SwaggerEndpoint("/swagger/v1/swagger.json", "...");
                });