Twitter RSS feed displays same tweet as recent despite updates

When I pull my Twitter RSS feed, it displays a tweet from 3 days ago and not my most recent one (I have updated 4 times since then.) After I update Twitter, both a feed pulled directly into a page and a feed that uses SimpleTwitter in WP display the newest tweet, but only for an hour or 2. Then return to the same old tweet from Thursday. This just began this morning.