RSS feed not showing – cache issue?

I am importing six RSS feeds from the same source. Five work fine, one refuses to import.

I don’t think it’s a plugin problem as the same has occurred with three different plugins.

And I don’t think there’s a problem with the feed as it checks out in Feedburner and works on other sites.

Could there be some kind of caching issue in my database that would prevent this one feed, and this one only, from importing? I can’t think how to troubleshoot it any further.

(Using WordPress 3.9.1)