X-plane.to, does not point to RSS

A new site has a feed here: https://x-plane.to/rss

And the error:

This address does not point to an RSS feed or a website with an RSS feed.

The feed was invalid, but they fixed it 12-24 hours ago (see validation here). I and others saw this error in 2016, I don’t know how to diagnose. Not sure if it’s cached or blocked or what.