`Run` returns `Unexpected token '<', "<!DOCTYPE "... is not valid JSON`

[xobs]

When going to https://play.rust-lang.org/?version=stable&mode=debug&edition=2021 in a new browser, hitting "Run" returns a compile error of:

Unexpected token '<', "<!DOCTYPE "... is not valid JSON

The actual response looks like a timeout error that the site is trying to parse as some sort of JSON message.