RSS doesn’t validate

It’s just been pointed out to me that the RSS feeds on a site launched today aren’t validating, and aren’t loading correctly in some RSS readers. For example, this feed:

https://www.newyorkoverheard.com/wp-rss2.php

Loads just fine in Thunderbird for me, but a friend can’t load it in his reader, and feedvalidator.org is reporting a “404: Not Found” error for that feed, even as it displays the entire feed and points out a few other code errors.

Would this indicate a problem with the WordPress installation, or is this a bug with a known fix?

Thanks!