Azure web app, custom status code description does not work

I deploy an ASP.NET to Azure web app. This web app have endpoint /usageinfo with custom status code description Below is the result in localhost:

However, the web app show different result:

Code

  return new HttpStatusCodeResult(usageInfo >= 95 ? 503 : 200,
                $"Account {BomEnvironment.EmbedUsername}. UsageInfo={usageInfo}");

Why are they different?

Thanks,