ASP.NET Core hosting environment variable ignored

Question

I have two web sites on my staging server, and both are ASP.NET Core sites that run in IIS. I have set the environment variable ASPNETCORE_ENVIRONMENT to Staging machine-wide. This works well for one of the sites, however the other ignores the variable and runs in production mode instead. I have to configure the hosting environment into the web.config file to run it in staging mode.

Why does one site not take the environment variable into account?

In both of my Startup(IHostingEnvironment env) constructors, I use the environment variables:

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
        .AddJsonFile("logging.json")
        .AddEnvironmentVariables();  //   <---
        Configuration = builder.Build();
    }

Answer 1

As said in this similar question, the trick was simply to set the app pool to load the user variables (IIS -> Server -> App Pools -> Right click on pool -> Set application pool defaults... -> Load User Profile = True).

I configured only one of my app pools accordingly, thus only one of the sites could access the environment variables.