Revise my question - why it returns 406 and an empty page if Discourse Meta is taken as a non exist page. 404 and an Oops message are more reasonable.
I see 406 response code from network tab in Chrome developer tools. I see a Oops page very occasionally. Displaying the Oops page is reasonable.
My question is no matter what errors are, it’s application’s responsibility to present a user friendly error message (like the Oops page does) rather than a blank page. I guess in case of 406 response, the application doesn’t even be reached. It’s an error reported by a service in front of application, that may be a web server or a proxy server.