Https://www.planetmountain.com/rss.lasso: Not an RSS feed

Hello,

the RSS feed from https://www.planetmountain.com/ recently started to not being recognized as a valid RSS feed. At a quick manual inspection it seems that the URL returns what looks like valid RSS to me. Is there a problem with the Newsblur parsing or did the website started producing invalid RSS? Is there a way to have more details about what goes wrong?

Thank you.

Cheers,
Dan