“Invalid feed URL”

Hi,

I use RSS Feed Aggregator to generate posts from 150 or so different feeds. Recently, one of the feeds stopped working: I get an “Invalid feed URL” error message and no items are imported. When I try to validate the feed, however, it says the RSS is valid:

https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.lesswrong.com%2Ffeed.xml

I happen to know the developers of the site which the feed is associated with, and they told me they haven’t tweaked the feed code recently. So the feed is valid, nothing about it has changed, and yet for some reason RSS Aggregator can no longer read it.

I updated the plugin to the latest version, deactivated all my other plugins, and changed the theme to WordPress’s default, but none of this helped.

The page I need help with: [log in to see the link]